Income Tax Disclosure [Abstract] Current: Current Federal, State and Local, Tax Expense (Benefit) [Abstract] U.S. – federal Current Federal Tax Expense (Benefit) U.S. – state and local Current State and Local Tax Expense (Benefit) Other than U.S. Current Foreign Tax Expense (Benefit) Total current Current Income Tax Expense (Benefit) Deferred: Deferred Federal, State and Local, Tax Expense (Benefit) [Abstract] U.S. – federal Deferred Federal Income Tax Expense (Benefit) U.S. – state and local Deferred State and Local Income Tax Expense (Benefit) Other than U.S. Deferred Foreign Income Tax Expense (Benefit) Total deferred Deferred Income Tax Expense (Benefit) Provision for Income Taxes Income Tax Expense (Benefit) Risks and Uncertainties [Abstract] Fair Value, Concentration of Risk [Table] Fair Value, Concentration of Risk [Table] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Government Contracts Concentration Risk Government Contracts Concentration Risk [Member] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Sales Revenue, Net Sales Revenue, Net [Member] Accounts Receivable Accounts Receivable [Member] Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] Concentration risk percentage Concentration Risk, Percentage Allowance for doubtful accounts receivable Allowance for Doubtful Accounts Receivable Retirement Benefits [Abstract] Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Pension Plan Pension Plan [Member] Other Benefits Other Postretirement Benefits Plan [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Amortization of prior service cost Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Recognized net actuarial loss (gain) Defined Benefit Plan Mark To Market Adjustment Defined benefit plan mark to market adjustment. Net periodic benefit cost (income) Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Segment Reporting [Abstract] Segment Reporting Segment Reporting Disclosure [Text Block] Statement of Comprehensive Income [Abstract] Tax (provision) benefit of unrealized losses on derivative financial instruments Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax Tax provision (benefit) on reclassification adjustment for losses on derivative financial instruments Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Tax benefit on unrecognized losses Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Tax benefit of recognition of benefit plan costs Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax Tax provision of unrealized gains Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Tax provision on reclassification adjustment for gain on investment Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Accounting Policies [Abstract] Deferred Finance Costs [Roll Forward] Deferred Finance Costs [Roll Forward] Deferred Finance Costs [Roll Forward] Balance at beginning of period Debt Issuance Costs, Net Additions Debt Issuance Costs, Gross Interest expense – debt issuance costs Amortization of Debt Issuance Costs Distributed in connection with the spin-off Deferred Finance Spinoff Related Costs Deferred finance spinoff related costs. Balance at end of period Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Schedule of Assumptions Used to Calculate Fair Value of Option Grant Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Summarized Activity of Stock Options Share-based Compensation, Stock Options, Activity [Table Text Block] Schedule of Restricted Stock Units Schedule of Nonvested Restricted Stock Units Activity [Table Text Block] Schedule of Summarized Activity of Stock Appreciation Schedule of Share-based Compensation, Stock Options and Stock Appreciation Rights Award Activity [Table Text Block] Currency translation adjustments Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax Net unrealized gain (loss) on derivative financial instruments Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax Unrecognized prior service cost on benefit obligations Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax Net unrealized gain on available-for-sale investments Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Schedule of Fair Value of Separate Accounts by Major Category of Investment [Table] Schedule of Fair Value of Separate Accounts by Major Category of Investment [Table] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Defined Benefit Plan, Asset Categories [Axis] Defined Benefit Plan, Asset Categories [Axis] Plan Asset Categories [Domain] Plan Asset Categories [Domain] Fixed Income Fixed Income Funds [Member] Equities Equity Funds [Member] Commingled and Mutual Funds Commingled And Mutual Funds [Member] Commingled and mutual funds. U.S. Government Securities Us Government Securities [Member] U.S. government securities. Partnerships with Security Holdings Partnerships With Security Holdings [Member] Partnerships with security holdings. Real Estate Real Estate [Member] Cash and Accrued Items Cash And Accrued Items [Member] Cash and accrued items. Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items] Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items] Total Assets Defined Benefit Plan, Fair Value of Plan Assets Unclassified Defined Benefit Plan, Alternative Investments, Fair Value of Plan Assets Defined Benefit Plan, Alternative Investments, Fair Value of Plan Assets Investments, Debt and Equity Securities [Abstract] Proceeds Proceeds from Sale of Available-for-sale Securities Gross Realized Gains Available-for-sale Securities, Gross Realized Gains Gross Realized Losses Available-for-sale Securities, Gross Realized Losses Equity Method Investments and Joint Ventures [Abstract] Revenues Equity Method Investment, Summarized Financial Information, Revenue Gross profit Equity Method Investment, Summarized Financial Information, Gross Profit (Loss) Net Income Equity Method Investment, Summarized Financial Information, Net Income (Loss) Pension Plans and Postretirement Benefits Pension and Other Postretirement Benefits Disclosure [Text Block] Asset retirement obligations Abstract Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Balance at beginning of period Asset Retirement Obligation Costs incurred Asset Retirement Obligation, Liabilities Settled Additions/adjustments Asset Retirement Obligation, Revision of Estimate Acquisition of NEC Asset Retirement Obligation, Business Acquisition Asset Retirement Obligation, Business Acquisition Accretion Asset Retirement Obligation, Accretion Expense Distributed in connection with the spin-off Asset Retirement Obligation Spin Off Asset retirement obligation spin off. Translation Asset Retirement Obligation, Foreign Currency Translation Gain (Loss) Balance at end of period Risks and Uncertainties Risks And Uncertainties [Text Block] Risks and uncertainties text block. Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common Stock Common Stock [Member] Capital In Excess of Par Value Additional Paid-in Capital [Member] Retained Earnings Retained Earnings [Member] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Treasury Stock Treasury Stock [Member] Stockholders' Equity Parent [Member] Noncontrolling Interest Noncontrolling Interest [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Balance (shares) Common Stock, Shares, Issued Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Dividends declared Dividends Currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Derivative financial instruments Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax Defined benefit obligations Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Available-for-sale investments Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Exercise of stock options (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Contributions to thrift plan Stock Issued During Period, Value, Employee Stock Purchase Plan Contributions to thrift plan (shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans Shares placed in treasury Treasury Stock, Value, Acquired, Cost Method Stock-based compensation charges Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Stock-based compensation charges (shares) Adjustments To Additional Paid In Capital Share Based Compensation Requisite Service Period Recognition Shares Adjustments to additional paid in capital share based compensation requisite service period recognition shares. Distributions to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Other Stockholders' Equity Note, Spinoff Transaction Deconsolidation of Generation mPower LLC Noncontrolling Interest, Decrease from Deconsolidation Other Stockholders' Equity, Other Balance Balance (shares) 2018 Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months 2019 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2020 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Five Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] U.S. Government and agency securities US Government Agencies Debt Securities [Member] Corporate bonds Corporate Bond Securities [Member] Equities Equity Securities [Member] Mutual funds Mutual Funds [Member] Mutual funds. Asset-backed securities and collateralized mortgage obligations Asset-backed Securities [Member] Commercial paper Commercial Paper [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring Fair Value, Measurements, Recurring [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Estimated Fair Value Trading Securities Available-for-sale securities measured at fair value Available-for-sale Securities Reconciliation of Unrecognized Tax Benefits Summary of Income Tax Contingencies [Table Text Block] Components of Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Income from Continuing Operations Before Provision for Income Taxes Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block] Components of Provision for Income Taxes Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Reconciliation of Income Tax Provision Related to Continuing Operations from U.S. Statutory Federal Tax Rate Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Valuation Allowance for Deferred Tax Assets Summary of Valuation Allowance [Table Text Block] Pension Plans Postretirement And Other Employee Benefits [Table] Pension Plans Postretirement And Other Employee Benefits [Table] Pension Plans Postretirement And Other Employee Benefits [Table] Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location [Domain] Retirement Plan Sponsor Location [Domain] UNITED STATES UNITED STATES Foreign Plan Foreign Plan [Member] Pension Plans, Postretirement and Other Employee Benefits [Line Items] Pension Plans, Postretirement and Other Employee Benefits [Line Items] Pension Plans, Postretirement and Other Employee Benefits [Line Items] Expected employer contributions to trusts of defined benefit plans, 2018 Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year Expected benefit payments, 2018 Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months Expected benefit payments, 2019 Defined Benefit Plan, Expected Future Benefit Payment, Year Two Expected benefit payments, 2020 Defined Benefit Plan, Expected Future Benefit Payment, Year Three Expected benefit payments, 2021 Defined Benefit Plan, Expected Future Benefit Payment, Year Four Expected benefit payments, 2022 Defined Benefit Plan, Expected Future Benefit Payment, Year Five Expected benefit payments, 2023-2027 Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] BWXT Stock Options Employee Stock Option [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Outstanding at beginning of period (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Granted (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures Exercised (shares) Cancelled/expired/forfeited (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Outstanding at end of period (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Outstanding at beginning of period (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Exercised (USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Cancelled/expired/forfeited (USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Outstanding at end of period (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Outstanding at end of period, weighted-average remaining contractual term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Outstanding at end of period, aggregate intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Exercisable at end of period, Number of options (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Exercisable at end of period, weighted-average exercise price (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Exercisable at end of period, weighted-average remaining contractual term Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Exercisable at end of period, aggregate intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Costs incurred less costs of revenue recognized Cost Incurred Less Cost Of Revenue Recognized Asset Cost incurred less cost of revenue recognized asset. Revenues recognized less billings to customers Revenue Recognized In Excess Of Billings To Customer Revenue recognized in excess of billings to customer. Contracts in progress Costs in Excess of Billings, Current Billings to customers less revenues recognized Billings Less Revenue Recognized Billings less revenue recognized. Costs incurred less costs of revenue recognized Cost Incurred Less Cost Of Revenue Recognized Liability Cost incurred less cost of revenue recognized liability. Advance billings on contracts Billings in Excess of Cost Equity [Abstract] Capital Stock Stockholders' Equity Note Disclosure [Text Block] Basis of Presentation and Significant Accounting Policies Basis of Presentation and Significant Accounting Policies [Text Block] Retainages expected to be collected within one year Contract Receivable Retainage, Next Twelve Months Retainages expected to be collected after one year Contract Receivable Retainage, after Next Twelve Months Total retainages Contract Receivable Retainage Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Accumulated Other Comprehensive Income Component Recognized Reclassification out of Accumulated Other Comprehensive Income [Member] Realized (loss) gain on derivative financial instruments Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Amortization of prior service cost on benefit obligations Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Realized gains on investments Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Revenues Revenues Cost of operations Cost of Revenue Selling, general and administrative expenses Selling, General and Administrative Expense Total before tax Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Other – net Other Income Expense Net Other income expense net. Provision for Income Taxes Net Income Obligations and Funded Status Schedule of Net Funded Status [Table Text Block] Components of Net Periodic Benefit Cost Schedule of Net Benefit Costs [Table Text Block] Recognized Net Actuarial Losses (Gains) Schedule Of Actuarial Gain Loss Table [Text Block] Schedule of actuarial gain loss table. Summary of Additional Information Schedule Of Changes In Accumulated Other Comprehensive Income Loss [Table Text Block] Schedule of changes in accumulated other comprehensive income (loss). Weighted Average Assumptions Schedule of Assumptions Used [Table Text Block] Assumed Health-Care Cost Trend Rates Schedule of Health Care Cost Trend Rates [Table Text Block] Effect of One-Percentage-Point Change in Assumed Health-Care Cost Trend Rates Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block] Plan Asset Allocations by Asset Category Schedule Of Asset Allocation By Asset Category [Table Text Block] Schedule of asset allocation by asset category. Target Allocation by Asset Class Schedule of Allocation of Plan Assets [Table Text Block] Summary of Total Investments Measured at Fair Value Schedule Of Investments Measured At Fair Value [Table Text Block] Tabular disclosure of one or more of the entity's schedule of fair value of plan assets for defined benefit or other postretirement plans. Cash Flows Schedule of Expected Benefit Payments [Table Text Block] Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table] Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Reportable Segments Operating Segments [Member] Adjustments and Eliminations Consolidation, Eliminations [Member] Corporate, Non-Segment Corporate, Non-Segment [Member] Segment Reconciling Items Segment Reconciling Items [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Nuclear Operations Group Nuclear Operations [Member] Nuclear operations. Nuclear Services Group Technical Services [Member] Technical services. Nuclear Power Group Nuclear Energy [Member] Nuclear energy. Other Segments Other Segments [Member] Segment Reporting, Other Significant Reconciling Item [Line Items] Segment Reporting, Other Significant Reconciling Item [Line Items] Operating income Operating Income (Loss) mPower Framework Agreement Loss Contingency, Loss in Period Income Related to Litigation Proceeds Gain (Loss) Related to Litigation Settlement Special Charges for Restructuring Activities Restructuring Charges Cost to spin-off Power Generation business Income From Continuing Operation Spin Off Related Costs Income from continuing operation spin off related costs. Mark to Market Adjustment Mark To Market Adjustments Mark To Market Adjustments Interest income Investment Income, Interest Interest expense Interest Expense Total Other Income (Expense) Other Nonoperating Income (Expense) Income before Provision for Income Taxes Schedule of Operating Results by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of Revenue Information from Products and Service Lines Revenue from External Customers by Products and Services [Table Text Block] Schedule of Revenues by Geographical Area Schedule of Revenue from External Customers Attributed to Foreign Countries by Geographic Area [Table Text Block] Schedule of Property, Plant and Equipment, Net by Geographical Area Schedule of Disclosure on Geographic Areas, Long-Lived Assets in Individual Foreign Countries by Country [Table Text Block] Schedule Of Amortized And Unamortized Intangible Assets [Table] Schedule Of Amortized And Unamortized Intangible Assets [Table] Schedule of amortized and unamortized intangible assets [Table] Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets, Major Class Name [Domain] Indefinite-lived Intangible Assets, Major Class Name [Domain] NRC category 1 license Nrc Category One License [Member] NRC category one license. Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Customer relationships Customer Relationships [Member] CNSC class 1B nuclear facility license Licensing Agreements [Member] Acquired backlog Order or Production Backlog [Member] Favorable operating lease Above Market Leases [Member] Unpatented technology Unpatented Technology [Member] Tradename Trade Names [Member] Patented technology Patented Technology [Member] All other Other Intangible Assets [Member] Schedule Of Amortized And Unamortized Intangible Assets [Line Items] Schedule Of Amortized And Unamortized Intangible Assets [Line Items] Schedule of amortized and unamortized intangible assets [Line Items] Amortized intangible assets Finite-Lived Intangible Assets, Gross Accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Net amortized intangible assets Finite-Lived Intangible Assets, Net Unamortized intangible assets Indefinite-Lived Intangible Assets (Excluding Goodwill) Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Current Reporting Status Entity Current Reporting Status Entity Voluntary Filers Entity Voluntary Filers Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Public Float Entity Public Float Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract] Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract] Discount rate Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate Discount rate to determine service cost Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate to Determine Service Cost Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate to Determine Service Cost Discount rate to determine interest cost Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate to Determine Interest Cost Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate to Determine Interest Cost Expected return on plan assets Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets Rate of compensation increase Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase U.S. Income (Loss) from Continuing Operations before Income Taxes, Domestic Other than U.S. Income (Loss) from Continuing Operations before Income Taxes, Foreign Business Combinations [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] NEC BWXT Nuclear Energy Canada Inc. [Member] BWXT Nuclear Energy Canada Inc. [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Accounts receivable – trade Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Accounts Receivables Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Accounts Receivables Accounts receivable – other Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Accounts Receivables Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Accounts Receivables Contracts in progress Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Contracts in Progress Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Contracts in Progress Other current assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Property, plant and equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Goodwill Goodwill Intangible assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Total assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Accounts payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable Accrued employee benefits Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Employee-related Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Employee-related Liabilities Accrued liabilities – other Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other Accrued Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other Accrued Accrued warranty expense Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Product Warranty Accrual Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Product Warranty Accrual Accumulated postretirement benefit obligation Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Accumulated Postretirement Benefit Obligation Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Accumulated Postretirement Benefit Obligation Environmental liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Accrued Environmental Loss Contingencies Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Accrued Environmental Loss Contingencies Pension liability Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Defined Benefit Pension Plan Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Defined Benefit Pension Plan Liabilities Other liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other Total liabilities assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Net assets acquired Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net Amount of tax deductible goodwill Business Acquisition, Goodwill, Expected Tax Deductible Amount Change in Accounting Estimate by Type [Axis] Change in Accounting Estimate by Type [Axis] Change in Accounting Estimate, Type [Domain] Change in Accounting Estimate, Type [Domain] Change in Assumptions for Pension Plans Change in Assumptions for Defined Benefit Plans [Member] Retirement Plan Name [Axis] Retirement Plan Name [Axis] Retirement Plan Name [Domain] Retirement Plan Name [Domain] BWXT Retirement Plan BWXT Retirement Plan [Member] BWXT Retirement Plan [Member] Thrift Plan Thrift Plan [Member] Thrift plan. Thrift Plan and MII Thrift Plan Thrift Plan And Mii Thrift Plan [Member] Thrift plan and MII thrift plan. Canadian Plans Canadian Plans [Member] Canadian plans. Range [Axis] Range [Axis] Range [Domain] Range [Domain] Maximum Maximum [Member] Increase (decrease) of service and interest cost Defined Benefit Plan, Increase (Decrease) of Service and Interest Cost Defined Benefit Plan, Increase (Decrease) of Service and Interest Cost Pension benefit obligations transferred Defined Benefit Plan Obligation Transfers Defined benefit plan obligation transfers. Pension settlement related charges Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement Other comprehensive loss as components of net periodic benefit cost for pension benefit in the current fiscal year Defined Benefit Plan Amounts Recognized In Net Periodic Pension Cost And Other Comprehensive Income Defined benefit plan amounts recognized in net periodic pension cost and other comprehensive income. Other comprehensive income as components of net periodic benefit cost for other benefit in the current fiscal year Defined Benefit Plan Amounts Recognized In Net Periodic Benefit Cost And Other Comprehensive Loss Income Defined benefit plan amounts recognized in net periodic benefit cost and other comprehensive loss income. Other comprehensive loss as components of net periodic benefit cost for pension benefit in the next fiscal year Expected Net Periodic Benefit Cost For Pension Benefits Expected To Be Recognized Over Next Fiscal Year Expected net periodic benefit cost for pension benefits expected to be recognized over next fiscal year. Other comprehensive income as components of net periodic benefit cost for other benefit in the next fiscal year Expected Net Periodic Benefit Cost For Other Postretirement Benefits Expected To Be Recognized Over Next Fiscal Year Expected net periodic benefit cost for other postretirement benefits expected to be recognized over next fiscal year. Expected return on plan assets Percentage of total assets Defined Benefit Plan Percentage Of Assets Defined benefit plan, percentage of total assets. Percentage of investment return on domestic plan assets Defined Benefit Plan Percentage Of Investment Return On Plan Assets Defined benefit plan, percentage of investment return on plan assets. Percentage of matching contribution by employer Defined Contribution Plan, Employer Matching Contribution, Percent of Match Participants' contributions as a percentage of compensation Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Employer contributions Defined Contribution Plan, Cost Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Cost of operations Operating Expense [Member] Selling, general and administrative expenses Selling, General and Administrative Expenses [Member] Other – net Other Expense [Member] Actuarial loss (gain) Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Losses (Gains) on Asset Disposals and Impairments, Net Gain (Loss) on Disposition of Assets Equity in income of investees Income (Loss) from Equity Method Investments Total Capital Expenditures Payments to Acquire Productive Assets Total Depreciation and Amortization Depreciation Depletion And Amortization Excluding Discontinued Operation Depreciation depletion and amortization excluding discontinued operation. Total Assets Assets Excluding Assets Related To Discontinued Operations Assets excluding assets related to discontinued operations. Total Investment in Unconsolidated Affiliates Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Spin-off Spin Off Policy [Text Block] Spin Off Policy [Text Block] Reportable Segments Segment Reporting, Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Investments Investment, Policy [Policy Text Block] Foreign Currency Translation Foreign Currency Transactions and Translations Policy [Policy Text Block] Contracts and Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Warranty Expense Standard Product Warranty, Policy [Policy Text Block] Asset Retirement Obligations and Environmental Clean-up Costs Asset Retirement Obligation and Environmental Cost [Policy Text Block] Research and Development Research and Development Expense, Policy [Policy Text Block] Pension Plans and Postretirement Benefits Pension and Other Postretirement Plans, Policy [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Inventories Inventory, Policy [Policy Text Block] Property, Plant and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Investments in Unconsolidated Affiliates Equity and Cost Method Investments, Policy [Policy Text Block] Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Intangible Assets Goodwill and Intangible Assets, Intangible Assets, Policy [Policy Text Block] Deferred Debt Issuance Costs Other Non Current Assets [Policy Text Block] Other non-current assets. Capitalization of Interest Cost Interest Capitalization, Policy [Policy Text Block] Cash and Cash Equivalents and Restricted Cash Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Derivative Financial Instruments Derivatives, Policy [Policy Text Block] Self-Insurance Self Insurance Reserve [Policy Text Block] Loss Contingencies Commitments and Contingencies, Policy [Policy Text Block] Stock-Based Compensation Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Recently Adopted and New Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Land Land [Member] Buildings Building [Member] Machinery and equipment Machinery and Equipment [Member] Property under construction Asset under Construction [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Property plant and equipment gross Property, Plant and Equipment, Gross Less accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Net Property, Plant and Equipment Property, Plant and Equipment, Net Investments Investment [Text Block] Quarterly Financial Information Disclosure [Abstract] Selected Quarterly Financial Information Quarterly Financial Information [Table Text Block] Discontinued Operations and Disposal Groups [Abstract] Condensed Cash Flow Statement [Table] Condensed Cash Flow Statement [Table] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Discontinued Operations, Disposed of by Sale Discontinued Operations, Disposed of by Sale [Member] Disposal Group Name [Axis] Disposal Group Name [Axis] Disposal Group Name [Domain] Disposal Group Name [Domain] Power Generation Business Power Generation Business [Member] Power Generation Business [Member] Condensed Cash Flow Statements, Captions [Line Items] Condensed Cash Flow Statements, Captions [Line Items] Non-cash items included in net income (loss): Disposal Group Including Discontinued Operation Adjustments Noncash Items To Reconcile Net Income (Loss) To Cash Provided By (Used In) Operating Activities [Abstract] Disposal Group Including Discontinued Operation Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Disposal Group Including Discontinued Operation Depreciation Depletion And Amortization Disposal group including discontinued operation depreciation depletion and amortization. Income (loss) of investees, net of dividends Disposal Group Including Discontinued Operation Income Loss From Equity Method Investments Net Of Dividends Or Distributions Disposal group including discontinued operation income loss from equity method investments net of dividends or distributions. Losses on asset disposals and impairments, net Disposal Group Including Discontinued Operation Gains Losses On Disposition Of Assets And Impairments Non-Cash Items Disposal Group Including Discontinued Operation Gains Losses On Disposition Of Assets And Impairments Non-Cash Items Purchases of property, plant and equipment Disposal Group Including Discontinued Operation Payments To Acquire Property Plant And Equipment Disposal group including discontinued operation payments to acquire property plant and equipment. Derivative Instruments and Hedging Activities Disclosure [Abstract] Summary of Derivative Financial Instruments Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Schedule of Effect of Derivative Instruments on Statements of Financial Performance Derivative Instruments, Gain (Loss) [Table Text Block] Capital Stock [Table] Capital Stock [Table] Capital Stock [Table] Weighted Average Weighted Average [Member] Share Repurchase Program [Axis] Share Repurchase Program [Axis] Share Repurchase Program [Domain] Share Repurchase Program [Domain] Accelerated Share Repurchase Agreement Accelerated Share Repurchase Agreement [Member] Accelerated Share Repurchase Agreement [Member] Share Repurchase Program Share Repurchase Program [Member] Share Repurchase Program [Member] Capital Stock [Line Items] Capital Stock [Line Items] Capital Stock [Line Items] Common stock at an aggregate purchase price Stock Repurchase Program, Authorized Amount Additional common stock at an aggregate purchase price Stock Repurchase Program Additional Authorized Amount For Share Repurchase Program Stock repurchase program additional authorized amount for share repurchase program. Accelerated share repurchase, settlement (payment) or receipt Accelerated Share Repurchases, Settlement (Payment) or Receipt Stock repurchased during period (shares) Stock Repurchased During Period, Shares Shares repurchased average price (USD per share) Accelerated Share Repurchases, Final Price Paid Per Share Common stock repurchased (shares) Treasury Stock, Shares, Acquired Common stock repurchased Stock repurchase program, remaining authorized repurchase amount Stock Repurchase Program, Remaining Authorized Repurchase Amount Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward] Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward] Balance at beginning of period Product Warranty Accrual, Current Additions Standard and Extended Product Warranty Accrual, Increase for Warranties Issued Acquisition of NEC Extended Product Warranty Accrual, Additions from Business Acquisition Expirations and other changes Standard and Extended Product Warranty Accrual, Increase (Decrease) for Preexisting Warranties Payments Standard and Extended Product Warranty Accrual, Decrease for Payments Translation Standard and Extended Product Warranty Accrual, Foreign Currency Translation Gain (Loss) Balance at end of period Discount to customers in satisfaction of warranty obligations Product Warranty Accrual Warrant Discount Product warranty accrual warrant discount. Financial Instruments with Concentrations of Credit Risk Concentration Risk Disclosure [Text Block] Quarterly Financial Data [Table] Quarterly Financial Data [Table] Quarterly Financial Data [Table] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] Bechtel Bechtel [Member] Bechtel [Member] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Unsuccessful Outcome of Framework Agreement Unsuccessful Outcome of Framework Agreement [Member] Unsuccessful Outcome of Framework Agreement [Member] Favorable Regulatory Action Favorable Regulatory Action [Member] Restructuring Plan [Axis] Restructuring Plan [Axis] Restructuring Plan [Domain] Restructuring Plan [Domain] Framework Agreement Framework Agreement [Member] Framework Agreement [Member] Quarterly Financial Data [Line Items] Quarterly Financial Data [Line Items] Quarterly Financial Data [Line Items] Income related to litigation proceeds Expense in income tax provision related to significant changes in U.S. tax laws Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit) Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit) Deconsolidation, gain (loss), amount Deconsolidation, Gain (Loss), Amount Loss contingency, loss period Gain related to fair value of performance guarantees Fair Value Of Performance Guarantees Fair value of performance guarantees. Loss contingency accrual, period increase (decrease) Loss Contingency Accrual, Period Increase (Decrease) Defined benefit plan, actuarial gain (loss) Current assets Equity Method Investment, Summarized Financial Information, Current Assets Noncurrent assets Equity Method Investment, Summarized Financial Information, Noncurrent Assets Total Assets Equity Method Investment, Summarized Financial Information, Assets Current liabilities Equity Method Investment, Summarized Financial Information, Current Liabilities Owners' equity Equity Method Investment Summarized Financial Information, Equity Total Liabilities and Owners' Equity Equity Method Investment, Summarized Financial Information, Liabilities and Equity Equity income based on stated ownership percentages Equity Method Investment, Underlying Equity in Net Assets Timing of GAAP and other adjustments Equity Method Investment, Difference Between Carrying Amount and Underlying Equity Cash Settled Performance Units Cash Settled Performance Shares [Member] Cash settled performance shares. Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Nonvested at beginning of period (shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Adjustment to assumed vesting percentage (shares) Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Adjustment To Assumed Vesting Share based compensation arrangement by share based payment award equity instruments other than options adjustment to assumed vesting. Granted (shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vested (shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Cancelled/forfeited (shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Nonvested at end of period (shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Nonvested at beginning of period, weighted-average grant date fair value (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Adjustment to assumed vesting percentage, weighted-average grant date fair value (USD per share) Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Adjustment To Assumed Vesting Weighted Average Grant Date Fair Value Share based compensation arrangement by share based payment award equity instruments other than options adjustment to assumed vesting weighted average grant date fair value. Granted, weighted-average grant date fair value (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Vested, weighted-average grant date fair value (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Cancelled/forfeited, weighted-average grant date fair value (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Nonvested at end of period, weighted-average grant date fair value (USD per share) Sales to Proceeds from Sale of Equity Method Investments Dividends received Proceeds from Equity Method Investment, Distribution Capital contributions, net of returns Proceeds from Equity Method Investment, Distribution, Return of Capital Income Tax Contingency [Table] Income Tax Contingency [Table] Income Tax Authority, Name [Axis] Income Tax Authority, Name [Axis] Income Tax Authority, Name [Domain] Income Tax Authority, Name [Domain] Canada Revenue Agency Canada Revenue Agency [Member] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Federal Domestic Tax Authority [Member] State State and Local Jurisdiction [Member] Income Tax Contingency [Line Items] Income Tax Contingency [Line Items] Canadian local statutory rate Effective Income Tax Rate Reconciliation, Statutory Rate, Percent Effective Income Tax Rate Reconciliation, Statutory Rate, Percent Gross unrecognized tax benefits, effective tax rate reduced Unrecognized Tax Benefits that Would Impact Effective Tax Rate Decrease in unrecognized tax benefits Decrease in Unrecognized Tax Benefits is Reasonably Possible Decrease in net deferred tax asset Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense U.S. federal statutory rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Valuation allowance for deferred tax asset Deferred Tax Assets, Valuation Allowance Decrease in valuation allowance Tax Cuts and Jobs Act, Incomplete Accounting, Change in Tax Rate, Valuation Allowance, Provisional Income Tax Benefit Tax Cuts and Jobs Act, Incomplete Accounting, Change in Tax Rate, Valuation Allowance, Provisional Income Tax Benefit Net operating loss carryforwards Operating Loss Carryforwards Net operating loss carryforwards, valuation allowance Operating Loss Carryforwards, Valuation Allowance Undistributed earnings of subsidiaries Undistributed Earnings, Basic Unrecognized deferred income tax liabilities Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability, Undistributed Earnings of Foreign Subsidiaries Debt Disclosure [Abstract] Components of Long-Term Debt Schedule of Debt [Table Text Block] Acquisitions Business Combination Disclosure [Text Block] Nonrecurring Adjustment [Axis] Nonrecurring Adjustment [Axis] Nonrecurring Adjustment [Domain] Nonrecurring Adjustment [Domain] Increase in Amortization Expense Increase in Amortization Expense [Member] Increase in Amortization Expense [Member] Elimination of Historical Interest Income Elimination of Historical Interest Income [Member] Elimination of Historical Interest Income [Member] Additional Interest Expense Associated with Incremental Borrowings Additional Interest Expense Associated with Incremental Borrowings [Member] Additional Interest Expense Associated with Incremental Borrowings [Member] Additional Accretion Additional Accretion [Member] Additional Accretion [Member] Additional Depreciation Expense Additional Depreciation Expense [Member] Additional Depreciation Expense [Member] Elimination of Recognized Acquisition Related Costs Acquisition-related Costs [Member] GEH-C GE Hitachi Nuclear Energy Canada Inc. [Member] GE Hitachi Nuclear Energy Canada Inc. [Member] Business combination, consideration transferred Business Combination, Consideration Transferred Business combination, consideration transferred, working capital adjustment Business Combination, Consideration Transferred, Working Capital Adjustments Business Combination, Consideration Transferred, Working Capital Adjustments Number of employees Business Acquisition, Number of Employees Business Acquisition, Number of Employees Number of operating facilities Business Acquisition, Number of Operating Facilities Business Acquisition, Number of Operating Facilities Purchase price allocation adjustment, contracts in progress Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Costs in Excess of Billings Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Costs in Excess of Billings Purchase price allocation adjustment, property, plant and equipment Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment Purchase price allocation adjustment, intangible assets Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles Purchase price allocation adjustment, goodwill Goodwill, Purchase Accounting Adjustments Revenues of acquiree since acquisition date Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual Earnings (loss) of acquiree since acquisition date, actual Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual Pro forma net income (loss) attributable to BWX Technologies, Inc. Business Acquisition, Pro Forma Net Income (Loss) Revenue from External Customers by Products and Services [Table] Revenue from External Customers by Products and Services [Table] Eliminations/Other Intersegment Eliminations [Member] Products and Services [Axis] Products and Services [Axis] Products and Services [Domain] Products and Services [Domain] Nuclear Component Program Nuclear Component Program [Member] Nuclear component program. Commercial Operations Commercial Operations [Member] Commercial operations. Nuclear Environmental Services Nuclear Environmental Services [Member] Nuclear Environmental Services [Member] Management & Operation Contracts of U.S. Government Facilities Management And Operation Contracts Of U S Government Facilities [Member] Management and operation contracts of U.S. government facilities. Nuclear Services and Advanced Reactor Design and Engineering Nuclear Services and Advanced Reactor Design and Engineering [Member] Nuclear Services and Advanced Reactor Design and Engineering [Member] Nuclear Services and Engineering Nuclear Services [Member] Nuclear services Nuclear Components Nuclear Equipment [Member] Nuclear equipment. Revenue from External Customer [Line Items] Revenue from External Customer [Line Items] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Derivatives Designated as Hedges Designated as Hedging Instrument [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Foreign Exchange Contracts Foreign Exchange Contract [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Accounts receivable – other Other Accounts Receivable [Member] Other accounts receivable. Other Assets Other Assets [Member] Accounts payable Accounts Payable [Member] Other Liabilities Other Liabilities [Member] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Cash Flow Hedging Cash Flow Hedging [Member] Revenues Sales [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Asset Derivatives Derivative Asset Liability Derivatives Derivative Liability Amount of gain (loss) recognized in other comprehensive income Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Cost of operations Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Contracts in Progress and Advance Billings Schedule Of Contracts In Progress And Advance Billings [Table Text Block] Tabular disclosure for advance billings on contracts and contracts in progress. Retainages on Contracts Schedule Of Retainages On Contract [Table Text Block] Tabular disclosure of amount billed to customers under long-term contracts or programs that have been withheld because of retainage provisions in a contract to be collected in (a) the next fiscal year following the latest fiscal year or (b) after the next fiscal year following the latest fiscal year. Accumulated Other Comprehensive Income Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Schedule of Amounts Reclassified from Accumulated Other Comprehensive Income Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] Summary of Changes in Carrying Amount of Accrued Warranty Expense Schedule of Product Warranty Liability [Table Text Block] Asset Retirement Obligations Schedule of Asset Retirement Obligations [Table Text Block] Property, Plant and Equipment Property, Plant and Equipment [Table Text Block] Changes in Carrying Amount of Goodwill Schedule of Goodwill [Table Text Block] Schedule of Intangible Assets Schedule Of Intangible Assets [Table Text Block] Tabular disclosure of assets, excluding financial assets and goodwill, lacking physical substance, by either major class or business segment. Changes in Carrying Amount of Intangible Assets Schedule Of Changes In Carrying Amount Of Other Intangible Assets [Table Text Block] Schedule of changes in carrying amount of other intangible assets. Estimated Amortization Expense Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Changes in Carrying Amount of Debt Issuance Costs Schedule of Other Assets, Noncurrent [Table Text Block] Schedule of Modified Retrospective Adoption for New Revenue Recognition Standard Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Deferred tax assets: Components of Deferred Tax Assets [Abstract] Pension liability Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions Accrued warranty expense Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Warranty Reserves Accrued vacation pay Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Compensated Absences Accrued liabilities for self-insurance (including postretirement health care benefits) Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Self Insurance Accrued liabilities for executive and employee incentive compensation Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities Environmental and products liabilities Deferred Tax Assets Environmental And Products Liabilities Deferred tax assets environmental and products liabilities. Investments in joint ventures and affiliated companies Deferred Tax Assets, Equity Method Investments Long-term contracts Deferred Tax Assets Long Term Contracts Deferred tax assets long-term contracts. State tax net operating loss carryforward Deferred Tax Assets, Operating Loss Carryforwards, Domestic Tax credit carryforward Deferred Tax Assets, Tax Credit Carryforwards Other Deferred Tax Assets, Other Total deferred tax assets Deferred Tax Assets, Gross Valuation allowance for deferred tax assets Deferred tax assets Deferred Tax Assets, Net of Valuation Allowance Deferred tax liabilities: Components of Deferred Tax Liabilities [Abstract] Property, plant and equipment Deferred Tax Liabilities, Property, Plant and Equipment Long-term contracts Deferred Tax Liabilities Long Term Contracts Deferred tax liabilities, long term contracts. Intangibles Deferred Tax Liabilities, Intangible Assets Other Deferred Tax Liabilities, Other Total deferred tax liabilities Deferred Tax Liabilities, Net Net deferred tax assets Deferred Tax Assets, Net Fixed Income (excluding U.S. Government Securities) Fixed Income Excluding U S Government Securities [Member] Fixed income (excluding U. S. government securities) Equity Securities and Commingled Mutual Funds Equity Securities And Commingled Mutual Funds [Member] Equity securities and commingled mutual funds. Other Other Asset Category [Member] Other. Total Defined Benefit Plan, Actual Plan Asset Allocations Summary of Financial Information Regarding Results of Operations Schedule Of Discontinued Operations Income Statement Table [Text Block] Schedule of discontinued operations income statement table. Selected Financial Information Regarding Cash Flows Included in Condensed Consolidated Statements of Cash Flows Schedule Of Discontinued Operations Cash Flow Statement Table [Text Block] Schedule of discontinued operations cash flow statement table. Income Statement [Abstract] Costs and Expenses: Costs and Expenses [Abstract] Research and development costs Research and Development Expense Losses (gains) on asset disposals and impairments, net Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property Selling, general and administrative expenses mPower framework agreement Income related to litigation proceeds Income Related To Litigation Proceeds Income related to litigation proceeds. Special charges for restructuring activities Costs to spin-off the Power Generation business Costs Incurred, Development Costs Total Costs and Expenses Costs and Expenses Equity in Income of Investees Operating Income Other Income (Expense): Nonoperating Income (Expense) [Abstract] Provision for Income Taxes Income from continuing operations before noncontrolling interest Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Income (loss) from discontinued operations, net of tax Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Net (Income) Loss Attributable to Noncontrolling Interest Net Income (Loss) Attributable to Noncontrolling Interest Net Income Attributable to BWX Technologies, Inc. Net Income (Loss) Attributable to Parent Amounts Attributable to BWX Technologies, Inc.'s Common Shareholders: Income Amounts Attributable to Parent, Disclosures [Abstract] Income from continuing operations, net of tax Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Income (loss) from discontinued operations, net of tax Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Basic: Earnings Per Share, Basic [Abstract] Income from continuing operations (USD per share) Income (Loss) from Continuing Operations, Per Basic Share Income (loss) from discontinued operations (USD per share) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share Net income attributable to BWX Technologies, Inc. (USD per share) Earnings Per Share, Basic Diluted: Earnings Per Share, Diluted [Abstract] Income from continuing operations (USD per share) Income (Loss) from Continuing Operations, Per Diluted Share Income (loss) from discontinued operations (USD per share) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share Net income attributable to BWX Technologies, Inc. (USD per share) Earnings Per Share, Diluted Shares used in the computation of earnings per share (Note 18): Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Schedule of Revenues from External Customers and Long-Lived Assets [Table] Schedule of Revenues from External Customers and Long-Lived Assets [Table] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] U.S. Canada CANADA China CHINA Romania ROMANIA All Other Countries All Other Countries [Member] All Other Countries [Member] Revenues from External Customers and Long-Lived Assets [Line Items] Revenues from External Customers and Long-Lived Assets [Line Items] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Scenario, Forecast Scenario, Forecast [Member] U. S. Equity Us Equity [Member] U.S. equity. Global Equity Global Equity [Member] Global equity. Target allocation by asset class Defined Benefit Plan, Plan Assets, Target Allocation, Percentage Summary of Combined Balance Sheet Information Equity Method Investment Combined Balance Sheet Information [Table Text Block] Tabular disclosure of equity method investments including combined summarized balance sheet information. Summary of Combined Income Statement Information Equity Method Investment Combined Income Statement Information [Table Text Block] Tabular disclosure of equity method investments including combined summarized income statement information. Reconciliation of Net Income to Equity in Income Equity Method Investment Reconciliation Of Net Income To Equity In Income [Table Text Block] Tabular disclosure of equity method investments, including the difference between recorded amount of an investment and the value of the underlying equity in the net assets. Schedule of Transactions with Unconsolidated Affiliates Investments in and Advances to Affiliates [Table Text Block] Statement of Cash Flows [Abstract] CASH FLOWS FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Non-cash items included in net income from continuing operations: Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization Income of investees, net of dividends Income (Loss) from Equity Method Investments, Net of Dividends or Distributions Losses on asset disposals and impairments Gains Losses On Disposition Of Assets And Impairments Amount of gain (loss) on disposition of assets and impairments. Gain on deconsolidation of Generation mPower LLC Impairment of investments Cost-method Investments, Other than Temporary Impairment Provision for (benefit from) deferred taxes Deferred Income Taxes and Tax Credits Recognition of (gains) losses for pension and postretirement plans Recognition Of Gains Losses For Pension And Postretirement Plans Recognition of gains losses for pension and postretirement plans. Stock-based compensation and thrift plan expense Share-based Compensation Changes in assets and liabilities, net of effects from acquisitions: Increase (Decrease) in Operating Capital [Abstract] Accounts receivable Increase (Decrease) in Accounts and Other Receivables Accounts payable Increase (Decrease) in Accounts Payable Contracts in progress and advance billings on contracts Increase Decrease Contracts In Progress And Advance Billings On Contracts Amount of increase (decrease) in the asset reflecting the cost incurred on uncompleted contracts in excess of related billings and the liability reflecting cash payments received before the related costs have been incurred. Income taxes Increase (Decrease) in Income Taxes Accrued and other current liabilities Increase (Decrease) in Other Accrued Liabilities Pension liability, accrued postretirement benefit obligation and employee benefits Increase Decrease In Pension Postretirement And Accrued Employee Benefits The increase (decrease) during the reporting period in the amount due to fund pension and non-pension benefits to employees, retired and disabled former employees, as well as the increase (decrease) during the period of accrued employee benefits. Other, net Increase (Decrease) in Other Operating Assets and Liabilities, Net NET CASH PROVIDED BY OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities CASH FLOWS FROM INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Decrease (increase) in restricted cash and cash equivalents Increase (Decrease) in Restricted Cash Purchases of property, plant and equipment Payments to Acquire Property, Plant, and Equipment Acquisition of businesses, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Purchases of securities Payments to Acquire Available-for-sale Securities Sales and maturities of securities Proceeds from Sale and Maturity of Available-for-sale Securities Proceeds from asset disposals Proceeds from Sales of Assets, Investing Activities Investments, net of return of capital, in equity method investees Payments to Acquire Assets, Investing Activities Other, net Payments for (Proceeds from) Other Investing Activities NET CASH USED IN INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities CASH FLOWS FROM FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Borrowings under Credit Agreement Proceeds from Issuance of Debt Repayments under Credit Agreement Repayments of Lines of Credit Payment of debt issuance costs Payments of Debt Issuance Costs Repurchase of common shares Payments for Repurchase of Common Stock Dividends paid to common shareholders Payments of Ordinary Dividends, Common Stock Exercise of stock options Proceeds from Stock Options Exercised Cash paid for shares withheld to satisfy employee taxes Payments Related to Tax Withholding for Share-based Compensation Cash divested in connection with spin-off of Power Generation business Cash Divested from Deconsolidation Other Proceeds from (Payments for) Other Financing Activities NET CASH USED IN FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities EFFECTS OF EXCHANGE RATE CHANGES ON CASH Effect of Exchange Rate on Cash and Cash Equivalents TOTAL INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS Cash and Cash Equivalents, Period Increase (Decrease) CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD Cash and Cash Equivalents, at Carrying Value, Including Discontinued Operations CASH AND CASH EQUIVALENTS AT END OF PERIOD SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION: Supplemental Cash Flow Information [Abstract] Cash paid during the period for: Cash Paid During Period For [Abstract] Cash Paid During Period For [Abstract] Interest Interest Paid, Net Income taxes (net of refunds) Income Taxes Paid, Net Income taxes (net of refunds) Noncash Investing and Financing Items [Abstract] Accrued capital expenditures included in accounts payable Capital Expenditures Incurred but Not yet Paid Increase (decrease) in accumulated other comprehensive income due to actuarial losses – before taxes Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax Other Comprehensive Income (Loss): Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] Derivative financial instruments: Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract] Unrealized gains (losses) arising during the period, net of tax (provision) benefit of $(264), $(209) and $1,786, respectively Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Reclassification adjustment for (gains) losses included in net income, net of tax provision (benefit) of $21, $86 and $(1,487), respectively Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Benefit obligations: Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract] Unrecognized losses arising during the period, net of tax benefit of $532, $606 and $381, respectively Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax Recognition of benefit plan costs, net of tax benefit of $(618), $(566) and $(581), respectively Other Comprehensive Income Defined Benefit Plans Net Gain Loss Recognized In Net Periodic Benefit Cost Net Of Tax Other comprehensive income defined benefit plans net gain loss recognized in net periodic benefit cost net of tax. Investments: Unrealized Gain (Loss) on Investments [Abstract] Unrealized (losses) gains arising during the period, net of tax provision of $(382), $(62) and $(4), respectively Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Reclassification adjustment for gains included in net income, net of tax provision of $223, $57 and $124, respectively Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax Other Comprehensive Income (Loss) Other Comprehensive Income (Loss), Net of Tax Total Comprehensive Income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive Income Attributable to Noncontrolling Interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Comprehensive Income Attributable to BWX Technologies, Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Statement of Financial Position [Abstract] ASSETS Assets [Abstract] Current Assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Restricted cash and cash equivalents Restricted Cash and Cash Equivalents Investments Short-term Investments Accounts receivable – trade, net Accounts Receivable, Net, Current Accounts receivable – other Other Receivables