Secured and Unsecured Debt of the Operating Partnership - Unsecured Senior Notes and Term Loan Facility (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2015	Jul. 01, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Principal amount			$ 172,500
Net carrying amount		$ 1,856,590	1,783,121
Unsecured Debt [Member] | Thirty Nine Million Unsecured Term Loan Due July 2019 [Member]
Debt Instrument [Line Items]
Net carrying amount		$ 39,000
Unsecured Senior Notes [Member] | Four Point Two Five Zero Percent Unsecured Senior Notes [Member] [Domain]
Debt Instrument [Line Items]
Stated interest rate		4.25%
Unsecured Senior Notes [Member] | 3.800% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	[1]	3.80%
Unsecured Senior Notes [Member] | 4.80% Unsecured Senior Notes due July 15, 2018 [Member]
Debt Instrument [Line Items]
Stated interest rate		4.80%
Unsecured Senior Notes [Member] | 6.625% Unsecured Senior Notes due June 1, 2020 [Member]
Debt Instrument [Line Items]
Stated interest rate		6.625%
Line of Credit [Member] | $150.0 Term Loan Facility [Member]
Debt Instrument [Line Items]
Net carrying amount		$ 150,000
Kilroy Realty, L.P. [Member]
Debt Instrument [Line Items]
Net carrying amount		1,856,590	1,783,121
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Net carrying amount		$ 1,667,590	1,594,121
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes [Member] | Four Point Three Seven Five Percent Unsecured Senior Notes [Member] [Domain] [Domain]
Debt Instrument [Line Items]
Stated interest rate	[2]	4.375%
Effective interest rate	[3]	4.44%
Principal amount		$ 400,000	0	$ 400,000
Unamortized discount		(2,159)		2,200
Net carrying amount		$ 397,841	0
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes [Member] | Four Point Two Five Zero Percent Unsecured Senior Notes [Member] [Domain]
Debt Instrument [Line Items]
Stated interest rate	[4]	4.25%
Effective interest rate	[3]	4.35%
Principal amount		$ 400,000	400,000
Unamortized discount		(4,050)	(4,348)		$ 4,472
Net carrying amount		$ 395,950	395,652
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes [Member] | 3.800% Unsecured Senior Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	[1]	3.80%
Effective interest rate	[3]	3.804%
Principal amount		$ 300,000	300,000
Unamortized discount		(70)	(79)
Net carrying amount		$ 299,930	299,921
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes [Member] | 4.80% Unsecured Senior Notes due July 15, 2018 [Member]
Debt Instrument [Line Items]
Stated interest rate	[1],[5]	4.80%
Effective interest rate	[3]	4.827%
Principal amount		$ 325,000	325,000
Unamortized discount		(191)	(265)
Net carrying amount		$ 324,809	324,735
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes [Member] | 6.625% Unsecured Senior Notes due June 1, 2020 [Member]
Debt Instrument [Line Items]
Stated interest rate	[6]	6.625%
Effective interest rate	[3]	6.743%
Principal amount		$ 250,000	250,000
Unamortized discount		(940)	(1,154)
Net carrying amount		$ 249,060	248,846
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes [Member] | 5.00% Unsecured Senior Notes due Nov 3, 2015 [Member]
Debt Instrument [Line Items]
Stated interest rate	[7]	5.00%
Effective interest rate	[3]	5.014%
Principal amount			325,000	0
Unamortized discount			(33)	0
Net carrying amount		$ 0	$ 324,967
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes [Member] | 6.45% Unsecured Senior Notes due Aug 4 2014 [Member]
Debt Instrument [Line Items]
Effective interest rate						6.45%	6.45%
Net carrying amount						$ 83,000
Kilroy Realty, L.P. [Member] | Line of Credit [Member] | $150.0 Term Loan Facility [Member]
Debt Instrument [Line Items]
Maturity date		Jul. 01, 2019	Jul. 01, 2019
Net carrying amount		$ 150,000	$ 150,000
Spread on variable rate	[8]	1.40%	1.56%
Kilroy Realty, L.P. [Member] | Line of Credit [Member] | Thirty Nine Million Unsecured Term Loan Due July 2019 [Member]
Debt Instrument [Line Items]
Net carrying amount				$ 39,000

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

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

[3] 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.

[4] Interest on these notes is payable semi-annually in arrears on February 15th and August 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 of 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 December 31, 2015 and December 31, 2014, respectively.