Unsecured Senior Notes (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Unsecured debt		$ 2,181,382	$ 1,783,121
Kilroy Realty, L.P. [Member]
Debt Instrument [Line Items]
Unsecured debt		$ 2,181,382	$ 1,783,121
Kilroy Realty, L.P. [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.05%	1.25%
Debt Instrument, Contingent Additional Borrowings		$ 311,000
Kilroy Realty, L.P. [Member] | Four Point Three Seven Five Percent Unsecured Senior Notes [Member] [Domain] [Domain] | Senior Notes [Member]
Debt Instrument [Line Items]
Stated coupon rate		4.375%
Effective interest rate		4.375%
Debt Instrument, Face Amount		$ 400,000	$ 0
Debt Instrument, Unamortized Discount		(2,215)	0
Unsecured debt		$ 397,785	0
Kilroy Realty, L.P. [Member] | Four Point Four Four Zero Percent Unsecured Senior Notes [Member] [Domain] [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Effective interest rate	[1],[2]	4.44%
Kilroy Realty, L.P. [Member] | Four Point Two Five Zero Percent Unsecured Senior Notes [Member] [Domain] | Senior Notes [Member]
Debt Instrument [Line Items]
Stated coupon rate		4.25%
Effective interest rate	[2],[3]	4.35%
Debt Instrument, Face Amount		$ 400,000	400,000
Debt Instrument, Unamortized Discount		(4,124)	(4,348)
Unsecured debt		$ 395,876	395,652
Kilroy Realty, L.P. [Member] | 3.800% Unsecured Senior Note [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Stated coupon rate		3.80%
Effective interest rate	[2],[4]	3.804%
Debt Instrument, Face Amount		$ 300,000	300,000
Debt Instrument, Unamortized Discount		(72)	(79)
Unsecured debt		$ 299,928	299,921
Kilroy Realty, L.P. [Member] | 4.800% Unsecured Senior Notes Due July Fifteen Two Thousand Eighteen [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Stated coupon rate		4.80%
Effective interest rate	[2],[4],[5]	4.827%
Debt Instrument, Face Amount		$ 325,000	325,000
Debt Instrument, Unamortized Discount		(209)	(265)
Unsecured debt		$ 324,791	324,735
Kilroy Realty, L.P. [Member] | 6.625% Unsecured Senior Notes due June 1 2020 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Stated coupon rate		6.625%
Effective interest rate	[2],[6]	6.743%
Debt Instrument, Face Amount		$ 250,000	250,000
Debt Instrument, Unamortized Discount		(994)	(1,154)
Unsecured debt		$ 249,006	248,846
Kilroy Realty, L.P. [Member] | 5.000% Unsecured Senior Notes due Nov3 2015 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Stated coupon rate		5.00%
Effective interest rate	[2],[7]	5.014%
Debt Instrument, Face Amount		$ 325,000	325,000
Debt Instrument, Unamortized Discount		(4)	(33)
Unsecured debt		$ 324,996	324,967
Kilroy Realty, L.P. [Member] | Term Loan Facility [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Maturity Date		Jul. 01, 2019
Unsecured debt		$ 150,000	$ 150,000
Debt Instrument, Basis Spread on Variable Rate	[8]	1.35%	1.56%

[1] Interest on these notes is payable semi-annually in arrears on April 1st and October 1st of each year.

[2] This represents the rate at which interest expense is recorded for financial reporting purposes, which reflects the amortization of initial issuance discounts, excluding debt issuance costs.

[3] Interest on these notes is payable semi-annually in arrears on February 15th and August 15th of each year.

[4] Interest on these notes is payable semi-annually in arrears on January 15th and July 15th of each year.

[5] In October 2015, certain common limited partners in the Operating Partnership that previously contributed their interests in the property at 6255 W. Sunset Blvd., Los Angeles, California to the Operating Partnership entered into an agreement with the Company. Pursuant to this agreement, such common limited partners will reimburse the Company for a portion of any amounts the Company may be required to pay pursuant to its guarantee of the Operating Partnership’s 4.800% Senior Notes due 2018 or that the Company may otherwise become required to pay under applicable law with respect to such notes.

[6] Interest on these notes is payable semi-annually in arrears on June 1st and December 1st of each year.

[7] Interest on these notes is payable semi-annually in arrears on May 3rd and November 3rd of each year.

[8] Our unsecured term loan facility interest rate was calculated based on an annual rate of LIBOR plus 1.150% and LIBOR plus 1.400% as of September 30, 2015 and December 31, 2014, respectively.