Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Face (par) amount of debt instrument at time of issuance.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Amount, after accumulated amortization, of debt discount.

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Amount of unamortized debt discount (premium) and debt issuance costs.

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The cash outflow to repay long-term debt that is not secured by collateral. Excludes repayments of tax exempt unsecured debt.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

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Secured and Unsecured Debt of the Operating Partnership - Unsecured Senior Notes (Details) - USD ($)	1 Months Ended	12 Months Ended
	Nov. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2015	Nov. 30, 2014
Debt Instrument [Line Items]
Debt instrument, face amount						$ 172,500,000
Repayments of unsecured debt		$ 0	$ 325,000,000	$ 83,000,000
Unsecured Debt [Abstract]
Outstanding borrowings (1)		1,847,351,000	1,844,634,000
Kilroy Realty, L.P. [Member]
Debt Instrument [Line Items]
Repayments of unsecured debt		0	325,000,000	$ 83,000,000
Unsecured Debt [Abstract]
Long-term debt, gross		2,333,766,000
Outstanding borrowings (1)		1,847,351,000	1,844,634,000
Kilroy Realty, L.P. [Member] \| Unsecured senior notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount		(6,600,000)
Unsecured Debt [Abstract]
Outstanding borrowings (1)		$ 1,659,167,000	1,656,776,000
3.475% unsecured senior notes [Member] \| Kilroy Realty, L.P. [Member] \| Unsecured senior notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount					$ 400,000,000
Debt Instrument, Unamortized Discount					$ (2,200,000)
3.48% unsecured senior notes due October 1, 2025 [Member] \| Unsecured senior notes [Member]
Unsecured Debt [Abstract]
Stated interest rate		4.375%
5.00% unsecured senior notes due November 2015 [Member] \| Unsecured senior notes [Member]
Debt Instrument [Line Items]
Repayments of unsecured debt	$ 325,000,000
Unsecured Debt [Abstract]
Stated interest rate					5.00%
4.375% unsecured senior notes [Member] \| Kilroy Realty, L.P. [Member] \| Unsecured senior notes [Member]
Unsecured Debt [Abstract]
Maturity date		Oct. 01, 2025
Stated interest rate		4.375%
Effective interest rate		4.44%
Long-term debt, gross		$ 400,000,000	400,000,000
Unamortized discount and deferred financing costs		4,846,000	5,400,000
Outstanding borrowings (1)		$ 395,154,000	394,600,000
4.25% unsecured senior notes [Member] \| Kilroy Realty, L.P. [Member] \| Unsecured senior notes [Member]
Unsecured Debt [Abstract]
Maturity date		Aug. 15, 2029
Stated interest rate		4.25%
Effective interest rate		4.35%
Long-term debt, gross		$ 400,000,000	400,000,000
Unamortized discount and deferred financing costs		6,696,000	7,228,000
Outstanding borrowings (1)		$ 393,304,000	392,772,000
3.800% unsecured senior notes [Member] \| Unsecured senior notes [Member]
Unsecured Debt [Abstract]
Stated interest rate		3.80%
3.800% unsecured senior notes [Member] \| Kilroy Realty, L.P. [Member] \| Unsecured senior notes [Member]
Unsecured Debt [Abstract]
Maturity date		Jan. 15, 2023
Stated interest rate		3.80%
Effective interest rate		3.804%
Long-term debt, gross		$ 300,000,000	300,000,000
Unamortized discount and deferred financing costs		1,656,000	1,931,000
Outstanding borrowings (1)		$ 298,344,000	298,069,000
4.80% unsecured senior notes due July 15, 2018 [Member] \| Unsecured senior notes [Member]
Unsecured Debt [Abstract]
Stated interest rate		4.80%
4.80% unsecured senior notes due July 15, 2018 [Member] \| Kilroy Realty, L.P. [Member] \| Unsecured senior notes [Member]
Unsecured Debt [Abstract]
Maturity date		Jul. 15, 2018
Stated interest rate		4.80%
Effective interest rate		4.827%
Long-term debt, gross		$ 325,000,000	325,000,000
Unamortized discount and deferred financing costs		767,000	1,251,000
Outstanding borrowings (1)		$ 324,233,000	323,749,000
6.625% unsecured senior notes due June 1, 2020 [Member] \| Unsecured senior notes [Member]
Unsecured Debt [Abstract]
Stated interest rate		6.625%
6.625% unsecured senior notes due June 1, 2020 [Member] \| Kilroy Realty, L.P. [Member] \| Unsecured senior notes [Member]
Unsecured Debt [Abstract]
Maturity date		Jun. 01, 2020
Stated interest rate		6.625%
Effective interest rate		6.743%
Long-term debt, gross		$ 250,000,000	250,000,000
Unamortized discount and deferred financing costs		1,868,000	2,414,000
Outstanding borrowings (1)		$ 248,132,000	$ 247,586,000