Revenue from Contract with Customer [Abstract] Revenue, Initial Application Period Cumulative Effect Transition [Table] Revenue, Initial Application Period Cumulative Effect Transition [Table] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Domain] Initial Application Period Cumulative Effect Transition [Domain] Difference between Revenue Guidance in Effect before and after Topic 606 Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2014-09 Accounting Standards Update 2014-09 [Member] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Net favorable changes in estimate that resulted in an increase in revenue Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price Cumulative effect of contract change, cost of operations Cumulative Effect of Contract Change Cost of Operations Cumulative effect of contract change cost of operations. Decrease in operating income from cumulative effect of contract changes Increase (Decrease) in Operating Income due to Adjustments to Contracts with Customers Increase (Decrease) in Operating Income due to Adjustments to Contracts with Customers Decrease in earnings per share from cumulative effect of contract changes Increase (Decrease) in Earnings Per Share due to Adjustments to Contracts with Customers Increase (Decrease) in Earnings Per Share due to Adjustments to Contracts with Customers Contracts in progress increase Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price Revenue recognized from advance billings on contracts Contract with Customer, Liability, Revenue Recognized Revenue from contract with customer Revenue from Contract with Customer, Excluding Assessed Tax Fair Value Disclosures [Abstract] Fair Value Measurements Fair Value Disclosures [Text Block] 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 Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding (in shares) Entity Common Stock, Shares Outstanding Statement of Comprehensive Income [Abstract] Net Income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss): Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] 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 [Abstract] Unrealized (losses) gains arising during the period, net of tax benefit (provision) of $24, $90, $(5) and $(149), 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 $7, $(71), $16 and $0, respectively Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Amortization of benefit plan costs, net of tax benefit of $(78), $(146), $(286) and $(459), respectively Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax Investments: Unrealized Gain (Loss) on Investments [Abstract] Unrealized losses arising during the period, net of tax benefit (provision) of $270, $(52), $270 and $(182), respectively Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Reclassification adjustment for losses (gains) included in net income, net of tax provision of $25, $5, $25 and $19, 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 Tax provision of unrealized gains on derivative financial instruments Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax Tax provision (benefit) on reclassification adjustment for (gains) losses on derivative financial instruments Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Tax benefit of amortization of benefit plan costs Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax Tax (provision) benefit of unrealized gains (losses) 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 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] Beginning balance (in shares) Common Stock, Shares, Issued Beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Recently adopted accounting standards Cumulative Effect of New Accounting Principle in Period of Adoption Dividends declared Dividends Currency translation adjustments 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 (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Shares placed in treasury Treasury Stock, Value, Acquired, Cost Method Stock-based compensation charges (in shares) Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Stock-based compensation charges Stock Granted, Value, Share-based Compensation, Net of Forfeitures Distributions to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Ending balance (in shares) Ending balance 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 Benefits Pension Plan [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Service cost Defined Benefit Plan, Service Cost Net periodic benefit (income) cost, excluding service costs Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Excluding Service Costs Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Excluding Service Costs Transfer of domestic pension benefit obligation to annuity contract Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement Number of retirees transferred to annuity contract Defined Benefit Plan, Number of Retirees Transferred to Annuity Contract Defined Benefit Plan, Number of Retirees Transferred to Annuity Contract Number of domestic pension plans Defined Benefit Plan, Number of Plans Defined Benefit Plan, Number of Plans Recognized net actuarial gain Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) Settlement loss Defined Benefit Plan, Plan Assets, Payment for Settlement Actuarial gain before settlement loss Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) Before Settlement Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) Before Settlement Contribution by employer Defined Benefit Plan, Plan Assets, Contributions by Employer Expected future employer contributions, remainder of fiscal year Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year Defined Benefit Plan [Abstract] Components of Net Periodic Benefit Cost Schedule of Net Benefit Costs [Table Text Block] Segment Reporting [Abstract] Segment Reporting Segment Reporting Disclosure [Text Block] Accounting Policies [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Restricted cash and cash equivalents Restricted Cash and Cash Equivalents, Current Restricted cash and cash equivalents included in Other Assets Restricted Cash and Cash Equivalents, Noncurrent Total cash and cash equivalents and restricted cash and cash equivalents as presented in our condensed consolidated statement of cash flows Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Movement in Product Warranty Accrual [Roll Forward] Movement in Standard Product Warranty Accrual [Roll Forward] Balance at beginning of period Product Warranty Accrual, Current Additions Standard and Extended Product Warranty Accrual, Increase for Warranties Issued 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 Dividends declared per share (in usd per share) Common Stock, Dividends, Per Share, Declared Calculated under Revenue Guidance in Effect before Topic 606 Calculated under Revenue Guidance in Effect before Topic 606 [Member] Assets Assets [Abstract] Contracts in progress Costs in Excess of Billings, Current Deferred Income Taxes Deferred Income Tax Assets, Net Liabilities Liabilities [Abstract] Accrued liabilities – other Other Accrued Liabilities, Current Advance billings on contracts Billings in Excess of Cost Stockholders' Equity Equity [Abstract] Retained earnings Retained Earnings (Accumulated Deficit) Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Adjustments and Eliminations Intersegment Eliminations [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Nuclear Operations Group Nuclear Operations [Member] Nuclear operations. Nuclear Services Group Nuclear Services Group [Member] Nuclear Services Group [Member] Nuclear Power Group Nuclear Power Group [Member] Nuclear Power Group [Member] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] UNITED STATES UNITED STATES CANADA CANADA Other Other [Member] Other [Member] Timing of Transfer of Good or Service [Axis] Timing of Transfer of Good or Service [Axis] Timing of Transfer of Good or Service [Domain] Timing of Transfer of Good or Service [Domain] Over-time Transferred over Time [Member] Point-in-time Transferred at Point in Time [Member] Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Domain] Contract with Customer, Basis of Pricing [Domain] Fixed-Price Incentive Fee Fixed-price Contract [Member] Firm-Fixed-Price Firm Fixed Price [Member] Firm Fixed Price [Member] Cost-Plus Fee Cost-Plus Fee [Member] Cost-Plus Fee [Member] Time-and-Materials Time-and-materials Contract [Member] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] Government Government [Member] Non-Government Non-Government [Member] Non-Government [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Revenues Revenues Business Combinations [Abstract] Acquisitions Business Combination Disclosure [Text Block] Fair Values Of Financial Instruments [Table] Fair Values Of Financial Instruments [Table] Fair Values Of Financial Instruments [Table] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] FX Forward Contracts Foreign Exchange Contract [Member] Fair Values Of Financial Instruments [Line Items] Fair Values Of Financial Instruments [Line Items] Fair Values Of Financial Instruments [Line Items] Fair value of foreign currency forward contracts Derivative, Fair Value, Net Statement of Financial Position [Abstract] ASSETS Current Assets: Assets, Current [Abstract] Investments Short-term Investments Accounts receivable – trade, net Accounts Receivable, Net, Current Accounts receivable – other Other Receivables Other current assets Other Assets, Current Total Current Assets Assets, Current Property, Plant and Equipment 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 Long Term Investments Excluding Investments In Unconsolidated Affiliates Long term investments excluding investments in unconsolidated affiliates. Goodwill Goodwill Investments in Unconsolidated Affiliates Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Intangible Assets Intangible Assets, Net (Excluding Goodwill) Other Assets Other Assets, Noncurrent TOTAL Assets LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity [Abstract] Current Liabilities: Liabilities, Current [Abstract] Current maturities of long-term debt Long-term Debt, Gross, Current Long-term Debt, Gross, Current Accounts payable Accounts Payable, Current Accrued employee benefits Employee-related Liabilities, Current Accrued warranty expense Total Current Liabilities Liabilities, Current Long-Term Debt Long-term Debt, Excluding Current Maturities Accumulated Postretirement Benefit Obligation Liability, Other Postretirement Defined Benefit Plan, Noncurrent Environmental Liabilities Accrued Environmental Loss Contingencies, Noncurrent Pension Liability Liability, Defined Benefit Pension Plan, Noncurrent Other Liabilities Other Liabilities, Noncurrent Commitments and Contingencies (Note 5) Commitments and Contingencies Stockholders' Equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Common stock, par value $0.01 per share, authorized 325,000,000 shares; issued 125,796,671 and 125,381,591 shares at September 30, 2018 and December 31, 2017, respectively Common Stock, Value, Issued Preferred stock, par value $0.01 per share, authorized 75,000,000 shares; No shares issued Preferred Stock, Value, Issued Capital in excess of par value Additional Paid in Capital, Common Stock Treasury stock at cost, 27,070,536 and 25,964,088 shares at September 30, 2018 and December 31, 2017, respectively Treasury Stock, Value Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Stockholders' Equity – BWX Technologies, Inc. Stockholders' Equity Attributable to Parent Noncontrolling interest Stockholders' Equity Attributable to Noncontrolling Interest Total Stockholders' Equity TOTAL Liabilities and Equity Cost of operations Cost of Revenue Operating Income Operating Income (Loss) Provision for Income Taxes Income Tax Expense (Benefit) Derivative Instruments and Hedging Activities Disclosure [Abstract] 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] Derivatives Not Designated as Hedges Not Designated as Hedging Instrument [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] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Asset Derivatives Derivative Asset Liability Derivatives Derivative Liability Derivative Instruments, Gain (Loss) [Table] Derivative Instruments, Gain (Loss) [Table] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Cash Flow Hedges Cash Flow Hedging [Member] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Revenues Sales [Member] Cost of operations Operating Expense [Member] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Amount of gain (loss) recognized in other comprehensive income Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Gain (loss) reclassified from accumulated other comprehensive income (loss) into earnings: effective portion Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Contract with Customer, Asset and Liability [Table] Contract with Customer, Asset and Liability [Table] Contract with Customer, Asset and Liability [Table] Contracts in Progress Contracts in Progress [Member] Contracts in Progress [Member] Accounts Receivable Accounts Receivable [Member] Contracts with Customers, Asset and Liability [Line Items] Contracts with Customers, Asset and Liability [Line Items] Contracts with Customers, Asset and Liability [Line Items] Contract with customer, asset Contract with Customer, Asset, Net, Current Advance billings on contracts Contract with Customer, Liability, Current Currency translation adjustments Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax Net unrealized gain 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 (loss) on available-for-sale investments Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Accumulated other comprehensive income Derivative Financial Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] 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 (Loss) Component Recognized Reclassification out of Accumulated Other Comprehensive Income [Member] Realized gain (loss) 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 gain (loss) 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] Cost of operations Income before Provision for Income Taxes 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 Basis Of Presentation And Significant Accounting Policies [Table] Basis Of Presentation And Significant Accounting Policies [Table] Basis of presentation and significant accounting policies [table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Sotera Health LLC's Nordion Medical Isotope Business Sotera Health LLC's Nordion Medical Isotope Business [Member] Sotera Health LLC's Nordion Medical Isotope Business [Member] 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] 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] Restricted Cash and Cash Equivalents [Axis] Restricted Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Cash Held for Future Decommissioning of Facilities Cash Held For Decommissioning Of Facilities [Member] Cash held for decommissioning of facilities. Cash Held to Meet Reinsurance Reserve Requirements Cash Held To Meet Reinsurance Reserve Requirements [Member] Cash held to meet reinsurance reserve requirements. Accounting Standards Update 2016-01 Accounting Standards Update 2016-01 [Member] Basis Of Presentation And Significant Accounting Policies [Line Items] Basis Of Presentation And Significant Accounting Policies [Line Items] Basis of presentation and significant accounting policies [line items] Number of reportable segments Number of Reportable Segments Number of components supplied to worldwide (more than) Number Of Large Heavy Components Supplied To Worldwide Number of large heavy components supplied to worldwide. Business combination, consideration transferred Business Combination, Consideration Transferred Number of personnel acquired Number of Personnel Acquired Number of Personnel Acquired Business acquisition, number of operating facilities Business Acquisition, Number of Operating Facilities Business Acquisition, Number of Operating Facilities Loss contingency as a result of the Framework Agreement Loss Contingency Accrual, Provision Accumulated other comprehensive income Total inventories Inventory, Net Restricted cash and cash equivalents Restricted Cash and Cash Equivalents Statutory tax rate for Canada operations Effective Income Tax Rate Reconciliation, Statutory Rate, Percent Effective Income Tax Rate Reconciliation, Statutory Rate, Percent Effective tax rate Effective Income Tax Rate Reconciliation, Percent Effective income tax rate reconciliation, share-based compensation cost (benefit) amount Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Amount Gross unrecognized tax benefits Unrecognized Tax Benefits Increase in cash and cash equivalents and restricted cash and cash equivalents Reconciliation of Revenue from Segments to Consolidated [Table] Reconciliation of Revenue from Segments to Consolidated [Table] Unallocated Corporate Corporate, Non-Segment [Member] Nuclear Services Group Nuclear Services [Member] Nuclear services Nuclear Power Group Nuclear Energy [Member] Nuclear energy. Other Other Segments [Member] Segment Reporting, Other Significant Reconciling Item [Line Items] Segment Reporting, Other Significant Reconciling Item [Line Items] Interest income Investment Income, Interest Interest expense Interest Expense Total Other Income (Expense) Other Nonoperating Income (Expense) Summary of Investments Measured at Fair Value Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Components of 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] Restricted Cash and Cash Equivalents Schedule of Cash and Cash Equivalents [Table Text Block] Restricted Cash and Cash Equivalents Restrictions on Cash and Cash Equivalents [Table Text Block] Summary of Changes in Carrying Amount of Accrued Warranty Expense Schedule of Product Warranty Liability [Table Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Line Items] Business Acquisition [Line Items] Revenues Business Acquisition, Pro Forma Revenue Net Income Attributable to BWX Technologies, Inc. Business Acquisition, Pro Forma Net Income (Loss) Basic Earnings per Common Share (in usd per share) Business Acquisition, Pro Forma Earnings Per Share, Basic Diluted Earnings per Common Share (in usd per share) Business Acquisition, Pro Forma Earnings Per Share, Diluted Schedule of Business Acquisition Assets Acquired and Liabilities Assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Schedule of Intangible Assets Acquired Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table Text Block] Schedule of Unaudited Pro Forma Financial Information Business Acquisition, Pro Forma Information [Table Text Block] Pension Plans and Postretirement Benefits Pension and Other Postretirement Benefits Disclosure [Text Block] Schedule of Operating Results by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract] Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract] Schedule of Initial Impact of the New Revenue Recognition Standard Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Schedule of Disaggregated Revenues Disaggregation of Revenue [Table Text Block] Schedule of Contract Assets and Liabilities Contract with Customer, Asset and Liability [Table Text Block] Schedule of Remaining Performance Obligations Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block] Condensed Income Statement [Table] Condensed Income Statement [Table] Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [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 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 Inventories Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory 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 Deferred Income Taxes Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets 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 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 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 Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Stock based compensation expense Allocated Share-based Compensation Expense Stock-based compensation, tax benefits Employee Service Share-based Compensation, Tax Benefit from Compensation Expense 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 Gains on asset disposals and impairments, net Gains Losses On Disposition Of Assets And Impairments Amount of gain (loss) on disposition of assets and impairments. Gain on forward contracts Gain (Loss) on Sale of Derivatives Recognition of debt issuance costs from Former Credit Facility Write off of Deferred Debt Issuance Cost Provision for deferred taxes Deferred Income Tax Expense (Benefit) 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 expense Share-based Compensation Changes in assets and liabilities: 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. 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Net Income (Loss) Attributable to Parent Earnings per Common Share: Basic: Earnings Per Share, Basic [Abstract] Net Income Attributable to BWX Technologies, Inc. (in usd per share) Earnings Per Share, Basic Diluted: Earnings Per Share, Diluted [Abstract] Net Income Attributable to BWX Technologies, Inc. (in usd per share) Earnings Per Share, Diluted Shares used in the computation of earnings per share (Note 10): 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 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 Financial Statements Derivative Instruments, Gain (Loss) [Table Text Block] Basic: Net Income (Loss) Available to Common Stockholders, Basic [Abstract] Net Income Attributable to BWX Technologies, Inc. Net Income (Loss) Available to Common Stockholders, Basic Weighted-average common shares (in shares) Basic earnings per common share (in usd per share) Diluted: Net Income (Loss) Available to Common Stockholders, Diluted [Abstract] Net Income Attributable to BWX Technologies, Inc. Net Income (Loss) Available to Common Stockholders, Diluted Effect of dilutive securities: Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract] Stock options, restricted stock units and performance shares (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Adjusted weighted-average common shares (in shares) Diluted earnings per common share (in usd per share) Number of shares that would be antidilutive (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Earnings Per Share Earnings Per Share [Text Block] Contingencies And Commitments [Table] Contingencies And Commitments [Table] Contingencies and commitments table Apollo and Parks Township Apollo And Parks Township [Member] Apollo and parks township. 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foreign currency forward contracts Derivative, Notional Amount Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] 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, 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] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Equities Equity Securities [Member] Mutual funds Mutual Fund [Member] U.S. Government and agency securities US Government Agencies Debt Securities [Member] Corporate bonds Corporate Bond Securities [Member] Asset-backed securities and collateralized mortgage obligations Asset-backed Securities [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] Equity securities Equity Securities, FV-NI Equity Securities, FV-NI Available-for-sale securities Available-for-sale Securities, Debt Securities Available-for-sale securities Available-for-sale Securities Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table] Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table] 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] Technical support agreement and relationship Technical Support Agreement and Relationship [Member] Technical Support Agreement and Relationship [Member] Unpatented technology Unpatented Technology [Member] Favorable operating leases Lease Agreements [Member] Customer relationship Customer Relationships [Member] Acquired Finite-Lived Intangible Assets [Line Items] Acquired Finite-Lived Intangible Assets [Line Items] Amount Finite-lived Intangible Assets Acquired Amortization Period Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Revenue Recognition Revenue from Contract with Customer [Text Block] Pension Benefits Other Benefits Other Postretirement Benefits Plan [Member] 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 (credit) Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Recognized net actuarial gain Net periodic benefit (income) cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Common stock, par value (in usd per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (in shares) Common Stock, Shares Authorized Common stock, shares issued (in shares) Preferred stock, par value (in usd per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Treasury stock at cost, shares (in shares) Treasury Stock, Shares 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] Additional Interest Expense Additional Interest Expense Associated with Incremental Borrowings [Member] Additional Interest Expense Associated with Incremental Borrowings [Member] Elimination of Acquisition Related Costs Acquisition-related Costs [Member] Revenues related to medical isotope business operations Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual Net Income related to medical isotope business operations Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual Adjustment to value of intangible assets Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles Adjustment to interest expense Business Combination, Pro Forma, Initial Accounting Incomplete, Adjustment, Interest Business Combination, Pro Forma, Initial Accounting Incomplete, Adjustment, Interest Acquisition related costs Business Combination, Acquisition Related Costs Basis of Presentation and Significant Accounting Policies Basis of Presentation and Significant Accounting Policies [Text Block]