Equity [Abstract] Stockholders' Equity of the Company Stockholders' Equity Note Disclosure [Text Block] Earnings Per Share [Abstract] Net income available to common stockholders Net Income (Loss) Available to Common Stockholders, Diluted [Abstract] Numerator: Numerator [Abstract] Numerator. Net income attributable to Kilroy Realty Corporation Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Allocation to participating securities Participating Securities, Distributed and Undistributed Earnings (Loss), Basic Numerator for basic and diluted net income available to common stockholders Net Income (Loss) Available to Common Stockholders, Basic and Diluted Net income (loss) after adjustments for preferred distributions and dividends and allocations to participating securities. Denominator: Earnings Per Common Unit, Denominator [Abstract] Earnings Per Common Unit - Denominator Basic weighted average vested shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Effect of dilutive securities (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment Diluted weighted average vested shares and common share equivalents outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Basic earnings per share: Earnings Per Share, Basic [Abstract] Net income available to common stockholders per share (in dollars per share) Earnings Per Share, Basic Diluted earnings per share: Earnings Per Share, Diluted [Abstract] Net income available to common stockholders per share (in dollars per share) Earnings Per Share, Diluted Fair Value Disclosures [Abstract] Fair Value Measurements and Disclosures Fair Value Disclosures [Text Block] Income Statement [Abstract] Statement [Table] Statement [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Kilroy Realty L.P. [Member] Kilroy Realty L.P. [Member] Kilroy Realty L.P. [Member] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Rental [Member] Rental [Member] Rental [Member] Tenant reimbursements [Member] Tenant Reimbursements [Member] Tenant Reimbursements [Member] Other property income [Member] Real Estate, Other [Member] Property [Member] Real Estate [Member] Statement [Line Items] Statement [Line Items] REVENUES (NOTE 1) Revenues [Abstract] Revenue Revenues EXPENSES Operating Expenses [Abstract] Property expenses Cost of Goods and Services Sold Real estate taxes Real Estate Tax Expense Provision for bad debts (Note 1) Provision for Doubtful Accounts Ground leases (Note 1 and 9) Operating Leases, Rent Expense General and administrative expenses General and Administrative Expense Leasing costs (Note 1) Operating Lease, Cost Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Total expenses Operating Expenses OTHER (EXPENSES) INCOME Nonoperating Income (Expense) [Abstract] Interest income and other net investment gain (Note 10) Interest Income And Other Net Investment Gain (Loss) Income derived from investments in debt and equity securities and on cash and cash equivalents and the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading. Interest income represents earnings which reflect the time value of money or transactions in which the payments are for the use or forbearance of money. Dividend income represents a distribution of earnings to shareholders by investee companies. Interest expense (Note 3) Interest Expense Total other (expenses) income Nonoperating Income (Expense) NET INCOME Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net income attributable to noncontrolling interests in consolidated property partnerships and subsidiaries Net Income (Loss) Attributable to Noncontrolling Interest NET INCOME AVAILABLE TO COMMON STOCKHOLDERS (UNITHOLDERS) Net Income (Loss) Available to Common Stockholders, Basic Net income available to common unitholders per unit-basic (in dollars per unit) Net income available to common unitholders per unit-diluted (in dollars per unit) Weighted average common shares outstanding – basic (in units) Weighted average common units outstanding - diluted (in units) Statement of Financial Position [Abstract] Common stock, par value (in dollars 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) Common Stock, Shares, Issued Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Statement of Stockholders' Equity [Abstract] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common Stock [Member] Common Stock [Member] Additional Paid-in Capital [Member] Additional Paid-in Capital [Member] Distributions in Excess of Earnings [Member] Accumulated Distributions in Excess of Net Income [Member] Total Stockholders' Equity [Member] Parent [Member] Noncontrolling Interests [Member] Noncontrolling Interest [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-02 [Member] Accounting Standards Update 2016-02 [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance (in shares) Beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Net income Cumulative adjustment Cumulative Effect of New Accounting Principle in Period of Adoption Issuance of share-based compensation awards Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Non-cash amortization of share-based compensation Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Settlement of restricted stock units for shares of common stock (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Gross Settlement of restricted stock units for shares of common stock Stock Issued During Period, Value, Restricted Stock Award, Gross Repurchase of common stock, stock options and restricted stock units (in shares) Shares Paid for Tax Withholding for Share Based Compensation Repurchase of common stock, stock options and restricted stock units Adjustments Related to Tax Withholding for Share-based Compensation Exchange of common units of the Operating Partnership (in shares) Stock Issued During Period, Shares, Conversion of Units Exchange of common units of the Operating Partnership Stock Issued During Period, Value, Conversion of Units Distributions to noncontrolling interests in consolidated property partnerships Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Adjustment for noncontrolling interest Adjustments to Additional Paid in Capital, Other Dividends declared per common share and common unit ($0.455 and $0.425 per share/unit for the three months ended March 31, 2019 and 2018, respectively) Dividends, Common Stock Ending balance (in shares) Ending balance Organization, Consolidation and Presentation of Financial Statements [Abstract] Consolidation policy Consolidation, Policy [Policy Text Block] Basis of accounting Basis of Accounting, Policy [Policy Text Block] New accounting pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Net income available to common stockholders Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Table] Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Table] 100 First LLC & 303 Second LLC [Member] 100 First LLC & 303 Second LLC [Member] 100 First LLC & 303 Second LLC [Member] Ownership [Axis] Ownership [Axis] Ownership [Domain] Ownership [Domain] 101 First LLC and 303 Second LLC [Member] 101 First LLC and 303 Second LLC [Member] 101 First LLC and 303 Second LLC [Member] Redwood LLC [Member] Redwood LLC [Member] Redwood LLC [Member] Kilroy Realty Finance, Inc. [Member] Kilroy Realty Finance, Inc. [Member] Kilroy Realty Finance, Inc. [Member] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Real estate investment [Member] Real Estate Investment [Member] Major Property Class [Axis] Major Property Class [Axis] Major Property Class [Domain] Major Property Class [Domain] Office properties [Member] Office Properties [Member] Office Properties [Member] Development properties [Member] Development Properties [Member] Development Properties [Member] Development sites [Member] Development Sites [Member] Development Sites [Member] Properties and development projects [Member] Properties and Development Projects [Member] Properties and Development Projects [Member] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Washington [Member] WASHINGTON San Francisco, California [Member] San Francisco, California [Member] San Francisco, California [Member] Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] Lease-up properties occupancy percentage Lease-Up Properties, Maximum Stabilized Occupacy, Percentage Lease-Up Properties, Maximum Stabilized Occupacy, Percentage Lease-up properties occupancy duration Lease-Up Properties, Maximum Stabilized Occupancy, Duration Lease-Up Properties, Maximum Stabilized Occupancy, Duration Number of Buildings Number of Real Estate Properties Area of land Area of Land Property ownership percentage Property Ownership Percentage Property Ownership Percentage Number of property partnerships Number of Property Partnerships Number of Property Partnerships Common general partnership interest in the Operating Partnership Noncontrolling Interest, Ownership Percentage by Parent Common limited partnership interest in the Operating Partnership Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Common general partnership interest in the Finance Partnership (percentage) Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest Percentage of limited partnership interest owned by Operating Partnership Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest Number of VIEs Variable Interest Entity, Number of Entities Variable Interest Entity, Number of Entities VIE assets Variable Interest Entity, Consolidated, Carrying Amount, Assets VIE liabilities Variable Interest Entity, Consolidated, Carrying Amount, Liabilities Noncontrolling interest in VIE Noncontrolling Interest in Variable Interest Entity Operating Lease, Lease Income Operating Lease, Lease Income Leasing costs Cumulative adjustment Number of Ground Leases Number of Ground Leases Number of Ground Leases Operating right of use ground lease asset Operating Lease, Right-of-Use Asset Operating ground lease liabilities Operating Lease, Liability Allowance for deferred rent receivables Allowance for deferred rent receivables Allowance for deferred rent receivables, attributable to, for instance, credit risk associated with a lessee. Number of Tenants Number Of Tenants Number of Tenants. Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract] Prepaid Expense and Other Assets [Abstract] Prepaid Expense and Other Assets [Abstract] Furniture, fixtures and other long-lived assets, net Furniture and Fixtures, Gross Note receivable Accounts and Notes Receivable, Net Prepaid expenses Prepaid Expense Total prepaid expenses and other assets, net Prepaid Expense and Other Assets Notes receivable, valuation allowance Allowance for Doubtful Accounts, Premiums and Other Receivables Subsequent Events [Abstract] Subsequent Events Subsequent Events [Text Block] Supplemental Cash Flow Elements [Abstract] SUPPLEMENTAL CASH FLOWS INFORMATION: Supplemental Cash Flow Information [Abstract] Cash paid for interest, net of capitalized interest of $18,901 and $13,051 as of March 31, 2019 and 2018, respectively Interest Paid, Excluding Capitalized Interest, Operating Activities Capitalized interest Interest Costs Capitalized Cash paid for amounts included in the measurement of ground lease liabilities Operating Lease, Payments NON-CASH INVESTING TRANSACTIONS: Noncash Investing Activities [Abstract] Noncash Investing Activities. Accrual for expenditures for operating properties and development properties Capital Expenditures Incurred but Not yet Paid Tenant improvements funded directly by tenants Tenant improvements funded directly by tenants to third parties The amount of cash paid directly to third parties by tenants for tenant improvements owned by the Company. NON-CASH FINANCING TRANSACTIONS: Noncash Financing Activities [Abstract] Accrual of dividends and distributions payable to common stockholders and common unitholders Common Stockholders And Unitholders Dividends And Distributions Declared But Not Paid Dividends and distributions declared but not paid to common stockholders and common unitholders. Exchange of common units of the Operating Partnership into shares of the Company’s common stock Conversion of Stock, Amount Converted Commitments and Contingencies Disclosure [Abstract] Long-term Purchase Commitment [Table] Long-term Purchase Commitment [Table] Lease Extension Options [Axis] Lease Extension Options [Axis] Lease Extension Options [Axis] Lease Extension Options [Domain] Lease Extension Options [Domain] Lease Extension Options [Domain] Ten year ground lease extension option [Member] Ten Year Ground Lease Extension Option [Member] Ten Year Ground Lease Extension Option [Member] Forty-five year ground lease extension option [Member] Forty-Five Year Ground Lease Extension Option [Member] Forty-Five Year Ground Lease Extension Option [Member] Environmental Remediation Contingency [Axis] Environmental Remediation Contingency [Axis] Environmental Remediation Contingency [Domain] Environmental Remediation Contingency [Domain] Environmental matters [Member] Environmental Matters [Member] Environmental Matters [Member] Long-term Purchase Commitment [Line Items] Long-term Purchase Commitment [Line Items] Commitments for contracts and executed leases, operating and redevelopment and development properties Other Commitment Number of extension options Number of Ground Lease Extension Options Number of extension options on ground lease. Ground lease extension option term Ground Lease Extension Option, Period Ground Lease Extension Option, Period Weighted average discount rate, ground leases Operating Lease, Weighted Average Discount Rate, Percent Weighted average remaining lease term Operating Lease, Weighted Average Remaining Lease Term Variable lease, cost Variable Lease, Cost Period after which ground lease rentals are adjusted based on fair market value and the Consumer Price Index Period for Ground lease rentals adjustment Period for Ground lease rentals adjustment. Annual ground lease rental obligations limit Annual Ground Lease Rental Obligations, Maximum Maximum annual ground lease rental obligations. Average annual percentage rent for previous five years (percent) Ground Lease, Minimum Rent Increase, Percentage of Annual Percentage Rent Ground Lease, Minimum Rent Increase, Percentage of Annual Percentage Rent for the previous 5 years Duration of ground lease prior to increase ten years Ground Lease, Minimum Rent Increase, Period of Increase Two Ground Lease, Minimum Rent Increase, Period of Increase Two Average annual percentage rent for previous ten years (percent) Ground Lease, Minimum Rent Increase, Percentage of Annual Percentage Rent Two Ground Lease, Minimum Rent Increase, Percentage of Annual Percentage Rent Two Accrued environmental remediation liabilities Accrual for Environmental Loss Contingencies Statement of Cash Flows [Abstract] CASH FLOWS FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization of real estate assets and leasing costs Depreciation, Depletion and Amortization Depreciation of non-real estate furniture, fixtures and equipment Depreciation, Nonproduction (Recoveries of) provision for bad debts and write-offs (Note 1) Provision for Doubtful Accounts, Including Tenant’s Lease Agreement Provision for Doubtful Accounts, Including Tenant’s Lease Agreement Non-cash amortization of share-based compensation awards Share-based Compensation Non-cash amortization of deferred financing costs and debt discounts and premiums Amortization of Debt Issuance Costs and Discounts Non-cash amortization of net below market rents Amortization of above and below Market Leases Non-cash amortization of deferred revenue related to tenant-funded tenant improvements Noncash amortization of deferred revenue related to tenant-funded tenant improvements The amortization of deferred revenue related to tenant funded tenant improvements during the period. Amortization of deferred revenue related to tenant funded tenant improvements is additional rental income over the term of the related lease and is added back to net income when calculating cash provided by (used in) operations using the indirect method. Straight-line rents Straight Line Rent Amortization of right of use ground lease assets Operating Lease, Right-of-Use Asset, Amortization Operating Lease, Right-of-Use Asset, Amortization Net change in other operating assets Increase (Decrease) in Operating Assets Net change in other operating liabilities Increase (Decrease) in Operating Liabilities 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] Expenditures for development properties and undeveloped land Payments to Develop Real Estate Assets Expenditures for operating properties Payments for Capital Improvements Expenditures for acquisition of operating properties Payments to Acquire Commercial Real Estate Net increase in acquisition-related deposits Payments for (Proceeds from) Deposits on Real Estate Acquisitions Proceeds received from repayment of note receivable Proceeds from Collection of Loans Receivable 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 on unsecured revolving credit facility (Note 3) Proceeds from Long-term Lines of Credit Repayments on unsecured revolving credit facility (Note 3) Repayments of Long-term Lines of Credit Borrowings on unsecured debt Proceeds from Unsecured Notes Payable Principal payments and repayments of secured debt (Note 3) Repayments of Secured Debt Financing costs Payments of Financing Costs Repurchase of common units and restricted stock units Payments Related to Tax Withholding for Share-based Compensation Distributions to noncontrolling interests in consolidated property partnerships Payments to Noncontrolling Interests Distributions paid to common unitholders Payments of Ordinary Dividends, Common Stock Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities Net decrease in cash and cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Cash and cash equivalents and restricted cash, beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash and cash equivalents and restricted cash, end of period Noncontrolling Interest [Abstract] Noncontrolling Interests on the Company's Consolidated Financial Statements Noncontrolling Interest Disclosure [Text Block] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Kilroy Realty 2006 Incentive Award Plan [Member] Kilroy Realty 2006 Incentive Award Plan [Member] Kilroy Realty 2006 Incentive Award Plan [Member] Executive Officer share-based compensation programs [Member] Executive Officer Share-Based Compensation Programs [Member] Executive Officer Share-Based Compensation Programs [Member] Market measure-based RSU estimate of probable [Member] Market Measure-Based RSU Estimate of Probable [Member] Market Measure-Based RSU Estimate of Probable [Member] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Restricted Stock Units (RSUs) [Member] Restricted Stock Units (RSUs) [Member] Market Measure-Based Restricted Stock Units (RSUs) [Member] Market Measure-Based Restricted Stock Units (RSUs) [Member] Market Measure-Based Restricted Stock Units (RSUs) [Member] Time-Based Restricted Stock Units (RSUs) [Member] Time-Based Restricted Stock Units (RSUs) [Member] Time-Based Restricted Stock Units (RSUs) [Member] 2019 Performance-Based RSUs [Member] 2019 Performance-Based RSUs [Member] 2019 Performance-Based RSUs [Member] 2019 Time-Based RSUs [Member] 2019 Time-Based RSUs [Member] 2019 Time-Based RSUs [Member] Time-Based Restricted Stock Units (RSUs), 2019 Time-Based RSU Grant [Member] Time-Based Restricted Stock Units (RSUs), 2019 Time-Based RSU Grant [Member] Time-Based Restricted Stock Units (RSUs), 2019 Time-Based RSU Grant [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Number of share-based incentive compensation plans Share-based Compensation Arrangement by Share-based Payment Award, Number of Plans Share-based Compensation Arrangement by Share-based Payment Award, Number of Plans Effective registration shares (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Number of shares available for grant Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Number of shares granted in period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Vesting, achievement of pre-set FFO per share goals, percentage of RSUs Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria Three Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria Three Vesting, Average debt to EBIDTA ratio, percentage of RSUs Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria One Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria One Vesting, Market measure, percentage of RSUs Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria Two Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria Two Capital shares reserved for future issuance (in shares) Common Stock, Capital Shares Reserved for Future Issuance Number of shares issuable per RSU Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Number of Shares Granted per Unit Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Number of Shares Granted per Unit Share price Share Price Fair value per share on valuation date Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Remaining expected life, including future volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term, Doubled Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term, Doubled Fair value per share on valuation date Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Fair value RSUs granted Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Grants In Period, Grant Date Fair Value The total fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans. Right to receive number of shares (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Share Rights Share-based Compensation Arrangement by Share-based Payment Award, Share Rights Share-based compensation expense Allocated Share-based Compensation Expense Share-based compensation expense capitalized Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount Share-based compensation not yet recognized Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Share-based compensation not yet recognized period of recognition Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 2018 Performance-Based RSUs [Member] 2018 Performance-Based RSUs [Member] 2018 Performance-Based RSUs [Member] Expected share price volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Schedule of Stock by Class [Table] At-The-Market Program [Member] 2018 At-The-Market Program [Member] 2018 At-The-Market Program [Member] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock [Domain] Sale of Stock [Domain] Forward equity sale [Member] Forward Equity Sale [Member] Forward Equity Sale [Member] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Scenario, forecast [Member] Scenario, Forecast [Member] Class of Stock [Line Items] At the market stock offering aggregate gross sales price of common stock At Market Stock Aggregate Gross Sales Price of Common Stock At Market Stock Aggregate Gross Sales Price of Common Stock Shares available for sale (in shares) Sale of Stock, Shares Available for Sale Sale of Stock, Shares Available for Sale Price per share (in dollars per share) Sale of Stock, Price Per Share At the market stock offering remaining amount available for issuance At Market Stock Offering Program Remained Available For Issuance At Market stock offering program remained available for issuance. Number of shares issued (in shares) Sale of Stock, Number of Shares Issued in Transaction Shares issued, value Common Stock, Value, Issued Earnings Per Unit [Abstract] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Numerator: Basic and diluted net loss income available to common unitholders [Abstract] Basic and diluted net (loss) income available to common unitholders. Net income attributable to Kilroy Realty, L.P. Allocation to participating securities Effect of dilutive securities (in units) Basic earnings per unit: Diluted earnings per unit: Partners' Capital Notes [Abstract] Schedule of Stock by Class [Table] Common units [Member] Capital Units [Member] Operating Partnership [Member] Operating Partnership [Member] Operating Partnership [Member] General Partners' Capital Account [Abstract] Company owned common units in the Operating Partnership General Partners' Capital Account, Units Outstanding Company owned general partnership interest Noncontrolling common units of the Operating Partnership Limited Partners' Capital Account, Units Outstanding Ownership interest of noncontrolling interest Net Income Available To Common Unitholders [Table] Net Income Available To Common Unitholders [Table] Net Income Available to Common Unitholders. Net Income Available To Common Unitholders [Line Items] Net Income Available To Common Unitholders [Line Items] Net Income Available To Common Unitholders. Net Income Available to Common Unitholders Per Unit of the Operating Partnership Earnings Per Share [Text Block] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] ASSETS Assets [Abstract] REAL ESTATE ASSETS: Real Estate Investment Property, Net [Abstract] Land and improvements Land and Land Improvements Buildings and improvements Investment Building and Building Improvements Undeveloped land and construction in progress Undeveloped Land and Construction in Progress The carrying amount of land and buildings available for development and redevelopment. Additionally, the current amount of expenditures for a real estate project that has not yet been completed. Total real estate assets held for investment Real Estate Investment Property, at Cost Accumulated depreciation and amortization Real Estate Investment Property, Accumulated Depreciation Total real estate assets held for investment, net Real Estate Investment Property, Net CASH AND CASH EQUIVALENTS Cash and Cash Equivalents, at Carrying Value RESTRICTED CASH Restricted Cash and Cash Equivalents MARKETABLE SECURITIES (Note 10) Debt Securities, Trading, and Equity Securities, FV-NI CURRENT RECEIVABLES, NET (Note 1) Accounts Receivable, Net DEFERRED RENT RECEIVABLES, NET (Note 1) Deferred Rent Receivables, Net DEFERRED LEASING COSTS AND ACQUISITION-RELATED INTANGIBLE ASSETS, NET (Note 1) Deferred Leasing Costs And Acquisition Related Intangible Assets Net This element represents (1) costs incurred by the lessor that are (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease. Those activities are: evaluating the prospective lessee's financial condition; evaluating and recording guarantees, collateral, and other security arrangements; negotiating lease terms; preparing and processing lease documents; and closing the transaction; (2) the identifiable intangible asset established upon acquisition based on a favorable difference between the terms of an acquired lease and the current market terms for that lease at the acquisition date; and (3) the amount of value allocated by a lessor (acquirer) to lease agreements which exist at acquisition of a leased property. This element is net of accumulated amortization. RIGHT OF USE GROUND LEASE ASSETS (Notes 1 and 9) PREPAID EXPENSES AND OTHER ASSETS, NET (Note 2) TOTAL ASSETS Assets LIABILITIES AND EQUITY Liabilities and Equity [Abstract] LIABILITIES: Liabilities [Abstract] Secured debt, net (Notes 3 and 10) Secured Debt Unsecured debt, net (Notes 3 and 10) Unsecured Debt Unsecured line of credit (Notes 3, 10 and 15) Long-term Line of Credit Accounts payable, accrued expenses and other liabilities Accounts Payable and Accrued Liabilities Ground lease liabilities (Notes 1 and 9) Accrued dividends and distributions (Note 15) Dividends Payable Deferred revenue and acquisition-related intangible liabilities, net Deferred Revenue And Acquisition Related Intangible Liabilities This element represents the (1) amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP; and (2) the liability associated with the acquisition of an off-market leases when the terms of the lease are unfavorable to the market terms for the lease at the date of acquisition. Rents received in advance and tenant security deposits Advance Rent, Including Tenant Security Deposits This element represents (1) money paid in advance to the lessor to protect against damage or nonpayment by the lessee during the term of the agreement; and (2) contractual amounts paid in advance by lessees. Total liabilities Liabilities COMMITMENTS AND CONTINGENCIES (Note 9) Commitments and Contingencies EQUITY: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Stockholders’ Equity (Note 4): Stockholders' Equity Attributable to Parent [Abstract] Common stock, $.01 par value, 150,000,000 shares authorized, 100,967,024 and 100,746,988 shares issued and outstanding, respectively Additional paid-in capital Additional Paid in Capital Distributions in excess of earnings (Note 1) Retained Earnings (Accumulated Deficit) Total stockholders’ equity Stockholders' Equity Attributable to Parent Noncontrolling Interests (Notes 1 and 5): Noncontrolling Interest Items [Abstract] Common units of the Operating Partnership Noncontrolling Interest in Operating Partnerships Noncontrolling interests in consolidated property partnerships Total noncontrolling interests Stockholders' Equity Attributable to Noncontrolling Interest Total equity TOTAL LIABILITIES AND EQUITY (CAPITAL) Liabilities and Equity Document and Entity Information [Abstract] 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 Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Emerging Growth Company Entity Emerging Growth Company Entity Small Business Entity Small Business Prepaid expenses and other assets, net Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Table Text Block] Other Significant Noncash Transactions [Table] Other Significant Noncash Transactions [Table] Other Significant Noncash Transactions [Line Items] Other Significant Noncash Transactions [Line Items] Schedule of supplemental cash flows Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Reconciliation of cash and cash equivalents and restricted cash Restrictions on Cash and Cash Equivalents [Table Text Block] Reconciliation of cash and cash equivalents and restricted cash Schedule of Cash and Cash Equivalents [Table Text Block] Schedule of Real Estate Properties [Table] Schedule of Real Estate Properties [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] Retail site [Member] Retail Site [Member] Stabilized Residential Properties [Member] Stabilized Residential Properties [Member] Stabilized Residential Properties [Member] In-process development projects - tenant improvement [Member] Development Projects - Tenant Improvement [Member] Development Projects - Tenant Improvement [Member] In-process development projects - under construction [Member] Development Projects - Under Construction [Member] Development Projects - Under Construction [Member] Production, Distribution and Repair (PDR) [Member] Production, Distribution and Repair (PDR) [Member] Production, Distribution and Repair (PDR) [Member] Real Estate Properties [Line Items] Real Estate Properties [Line Items] Rentable Square Feet Net Rentable Area Percentage Occupied Real Estate Properties, Percentage Occupied Real Estate Properties, Percentage Occupied Percentage Leased Real Estate Properties, Percentage Leased Real Estate Properties, Percentage Leased Number of Units Number of Units in Real Estate Property Number of residential units Number of Residential Units Number of Residential Units Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Line Items] Debt Instrument [Line Items] Unsecured revolving credit facility Schedule of Line of Credit Facilities [Table Text Block] Schedule of debt maturities Schedule of Maturities of Long-term Debt [Table Text Block] Capitalized interest and loan fees Capitalized Interest And Loan Fees [Table Text Block] Capitalized interest and loan fees. Supplemental Cash Flow Information of the Operating Partnership Cash Flow, Supplemental Disclosures [Text Block] Line of Credit Facility [Table] Line of Credit Facility [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Revolving credit facility [Member] Revolving Credit Facility [Member] Line of credit [Member] Line of Credit [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] $150 Million Term Loan Facility [Member] One Hundred Fifty Million Term Loan Facility [Member] One Hundred Fifty Million Term Loan Facility [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] London Interbank Offered Rate (LIBOR) [Member] London Interbank Offered Rate (LIBOR) [Member] Terms of the Credit Facility Line of Credit Facility [Abstract] Outstanding borrowings Remaining borrowing capacity Line of Credit Facility, Remaining Borrowing Capacity Total borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Interest rate (percent) Line of Credit Facility, Interest Rate at Period End Facility fee-annual rate (percent) Line of Credit Facility, Commitment Fee Percentage Undawn facility fee-annual rate (percent) Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Contingent additional borrowings Debt Instrument, Contingent Additional Borrowings Debt Instrument, Contingent Additional Borrowings Variable rate (percent) Debt Instrument, Basis Spread on Variable Rate Unamortized deferred financing costs Unamortized Debt Issuance Expense Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Unsecured senior notes [Member] Senior Notes [Member] Secured debt [Member] Secured Debt [Member] Stated debt maturities and scheduled amortization payments, excluding debt discounts Long-term Debt, Fiscal Year Maturity [Abstract] Remaining 2019 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months 2020 Long-term Debt, Maturities, Repayments of Principal in Year Two 2021 Long-term Debt, Maturities, Repayments of Principal in Year Three 2022 Long-term Debt, Maturities, Repayments of Principal in Year Four 2023 Long-term Debt, Maturities, Repayments of Principal in Year Five Thereafter Long-term Debt, Maturities, Repayments of Principal after Year Five Total debt Long-term Debt, Gross Unamortized deferred financing costs Unamortized discount Debt Instrument, Unamortized Discount Summary of real estate properties Schedule of Real Estate Properties [Table Text Block] Dividends declared per common unit (in dollars per unit) Distributions Per Limited Partnership and General Partnership Unit, Outstanding, Basic Share-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Noncontrolling Interest [Table] Noncontrolling Interest [Table] Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] Common units outstanding held by common limited partners Number of trading days Debt Instrument, Convertible, Threshold Trading Days Aggregate value upon redemption of outstanding noncontrolling common units Redeemable Noncontrolling Interest, Equity, Common, Fair Value 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 [Member] Fair Value, Measurements, Recurring [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Fair value (Level 1) [Member] Fair Value, Inputs, Level 1 [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] Assets and Liabilities Reported at Fair Value Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract] Marketable securities Assets, Fair Value Disclosure Fair value adjustment of marketable securities and deferred compensation plan liability Fair Value, Adjustment Disclosure [Abstract] Net gain (loss) on marketable securities Marketable Securities, Gain (Loss), Excluding Other-than-temporary Impairment Loss Leases [Abstract] Future Minimum Rent Lessor, Operating Leases [Text Block] Secured and Unsecured Debt of the Operating Partnership Debt Disclosure [Text Block] Net Income Available to Common Stockholders Per Share of the Company Schedule of share-based payment award, restricted stock units, valuation assumptions Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Preferred Units by Name [Axis] Preferred Units by Name [Axis] Preferred Units, Class [Domain] Preferred Units, Class [Domain] General partner, units issued General Partners' Capital Account, Units Issued General partners, units outstanding Limited partners, units issued Limited Partners' Capital Account, Units Issued 6.05% Mortgage Payable Due June 1, 2019 [Member] 6.05% Mortgage Payable Due June 1, 2019 [Member] 6.05% Mortgage Payable Due June 1, 2019 [Member] Repayments of Notes Payable Repayments of Notes Payable Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Carrying value [Member] Reported Value Measurement [Member] Fair value [Member] Estimate of Fair Value Measurement [Member] Unsecured debt [Member] Unsecured Debt [Member] Fair value (level 2) [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair value of debt, net Debt Instrument, Fair Value Disclosure Partners Capital Common Unit [Member] Partners Capital Common Unit [Member] Partners Capital Common Unit. Beginning balance (in units) Partners' Capital Account, Units Beginning balance Partners' Capital, Including Portion Attributable to Noncontrolling Interest Issuance of share-based compensation awards Partners' Capital Account, Unit-based Compensation Settlement of restricted stock units (in units) Partners' Capital Account, Units, Converted Exercise of stock options Repurchase of common units, stock options and restricted stock units (in units) Partners' Capital Account, Units, Treasury Units Purchased Repurchase of common units, stock options and restricted stock units Partners' Capital Account, Treasury Units, Purchased Distributions declared per common unit ($0.455 and $0.425 per unit for the three months ended March 31, 2019 and 2018, respectively) General Partners' Capital Account, Period Distribution Amount Ending balance (in units) Ending balance Fair value of the company's marketable securities Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Net gain (loss) on marketable securities Realized Gain (Loss) on Investments [Table Text Block] Carrying value and fair value of company's remaining financial instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Schedule of contractual expiration dates for ground leases Lessee, Operating Leases [Text Block] Schedule of future minimum rental repayments for ground leases Lessee, Operating Lease, Liability, Maturity [Table Text Block] Property expenses (Note 1) Ground leases (Notes 1 and 9) Interest expense (Note 3) Net income attributable to noncontrolling common units of the Operating Partnership Noncontrolling Interest in Net Income (Loss) Operating Partnerships, Redeemable Net income attributable to noncontrolling interests in consolidated property partnerships Net Income (Loss) Attributable to Noncontrolling Interest in Consolidated Subsidiary Net Income (Loss) Attributable to Noncontrolling Interest in Consolidated Subsidiary Total income attributable to noncontrolling interests Net income available to common stockholders per share – basic (in dollars per share) Net income available to common stockholders per share – diluted (in dollars per share) Weighted average common shares outstanding – basic (in shares) Weighted average common shares outstanding – diluted (in shares) Supplemental Cash Flow Information of the Company Future contractual minimum rent under operating lease Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract] Remaining 2019 Lessor, Operating Lease, Payments to be Received, Remainder of Fiscal Year 2020 Lessor, Operating Lease, Payments to be Received, Two Years 2021 Lessor, Operating Lease, Payments to be Received, Three Years 2022 Lessor, Operating Lease, Payments to be Received, Four Years 2023 Lessor, Operating Lease, Payments to be Received, Five Years 2024 Lessor, Operating Lease, Payments to be Received, Six Years Lessor, Operating Lease, Payments to be Received, Six Years Thereafter Lessor, Operating Lease, Payments to be Received, After Year Six Lessor, Operating Lease, Payments to be Received, After Year Six Total Lessor, Operating Lease, Payments to be Received Future contractual minimum rent under operating lease Operating Leases, Future Minimum Payments Receivable [Abstract] 2019 Operating Leases, Future Minimum Payments Receivable, Current 2020 Operating Leases, Future Minimum Payments Receivable, in Two Years 2021 Operating Leases, Future Minimum Payments Receivable, in Three Years 2022 Operating Leases, Future Minimum Payments Receivable, in Four Years 2023 Operating Leases, Future Minimum Payments Receivable, in Five Years Thereafter Operating Leases, Future Minimum Payments Receivable, Thereafter Total Operating Leases, Future Minimum Payments Receivable Borrowings on unsecured revolving credit facility (Note 3) Borrowings on unsecured debt Repurchase of common stock and restricted stock units Dividends and distributions paid to common stockholders and common unitholders Partners’ Capital of the Operating Partnership Partners' Capital Notes Disclosure [Text Block] Organization, Ownership and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Schedule of Common Units Outstanding Redeemable Noncontrolling Interest [Table Text Block] Future contractual minimum rent under operating leases Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block] Minimum commitment under our ground leases Operating Lease Liabilities, Payments Due [Abstract] Remaining 2019 Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year 2020 Lessee, Operating Lease, Liability, Payments, Due Year Two 2021 Lessee, Operating Lease, Liability, Payments, Due Year Three 2022 Lessee, Operating Lease, Liability, Payments, Due Year Four 2023 Lessee, Operating Lease, Liability, Payments, Due Year Five 2024 Lessee, Operating Lease, Liability, Payments, Due Year Six Lessee, Operating Lease, Liability, Payments, Due Year Six Thereafter Lessee, Operating Lease, Liability, Payments, Due After Year Six Lessee, Operating Lease, Liability, Payments, Due After Year Six Total Lessee, Operating Lease, Liability, Payments, Due Present value discount Lessee, Operating Lease, Liability, Undiscounted Excess Amount Minimum commitment under our ground leases Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2019 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2020 Operating Leases, Future Minimum Payments, Due in Two Years 2021 Operating Leases, Future Minimum Payments, Due in Three Years 2022 Operating Leases, Future Minimum Payments, Due in Four Years 2023 Operating Leases, Future Minimum Payments, Due in Five Years Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Total Operating Leases, Future Minimum Payments Due SUPPLEMENTAL CASH FLOWS INFORMATION: Cash paid for interest, net of capitalized interest of $18,901 and $13,051 as of March 31, 2019 and 2018, respectively NON-CASH INVESTING TRANSACTIONS: Accrual for expenditures for operating properties and development properties Tenant improvements funded directly by tenants NON-CASH FINANCING TRANSACTIONS: Accrual of distributions payable to common unitholders Subsequent Event [Table] Subsequent Event [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent event [Member] Subsequent Event [Member] Subsequent Event [Line Items] Subsequent Event [Line Items] Payment of dividend Prepaid Expenses and Other Assets, Net Other Assets Disclosure [Text Block] Cash and cash equivalents Restricted cash Cash and cash equivalents and restricted cash Dividends declared per common share and common unit (in dollars per share) Common Stock, Dividends, Per Share, Declared Capitalized Interest and Loan Fees [Table] Capitalized Interest and Loan Fees [Table] Capitalized Interest and Loan Fees [Table] Capitalized Interest and Loan Fees [Line Items] Capitalized Interest and Loan Fees [Line Items] [Line Items] for Capitalized Interest and Loan Fees [Table] Gross interest expense Interest Costs Incurred Capitalized interest and deferred financing costs Interest Costs Capitalized Adjustment Interest expense Land and improvements CASH AND CASH EQUIVALENTS MARKETABLE SECURITIES (Note 10) CURRENT RECEIVABLES, NET (Notes 1) DEFERRED RENT RECEIVABLES, NET (Notes 1) DEFERRED LEASING COSTS AND ACQUISITION-RELATED INTANGIBLE ASSETS, NET (Note 1) RIGHT OF USE GROUND LEASE ASSETS (Notes 1 and 9) PREPAID EXPENSES AND OTHER ASSETS, NET (Note 2) LIABILITIES AND CAPITAL LIABILITIES: Secured debt, net (Notes 3 and 10) Unsecured debt, net (Notes 3 and 10) Unsecured line of credit (Notes 3, 10 and 15) Accounts payable, accrued expenses and other liabilities Accrued distributions (Note 15) Deferred revenue and acquisition-related intangible liabilities, net Rents received in advance and tenant security deposits COMMITMENTS AND CONTINGENCIES CAPITAL: Common units, 100,967,024 and 100,746,988 held by the general partner and 2,023,287 and 2,025,287 held by common limited partners issued and outstanding, respectively (Note 6) General Partners' Capital Account Noncontrolling interests in consolidated property partnerships and subsidiaries (Note 1) Partners' Capital Attributable to Noncontrolling Interest Total capital