Secured and Unsecured Debt of the Operating Partnership - Unsecured Term Loan Facility (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Unsecured debt		$ 1,845,313	$ 1,844,634
Kilroy Realty, L.P. [Member]
Line of Credit Facility [Line Items]
Unsecured debt		1,845,313	1,844,634
Unamortized deferred financing costs		12,500
Kilroy Realty, L.P. [Member] | Line of Credit [Member] | $150 Million Term Loan Facility due July 2019 [Member]
Line of Credit Facility [Line Items]
Unsecured debt	[1]	$ 150,000	$ 150,000
Effective interest rate (percent)	[2]	1.59%	1.40%
Maturity date		Jul. 01, 2019	Jul. 01, 2019
Unamortized deferred financing costs		$ 900	$ 900
Kilroy Realty, L.P. [Member] | Line of Credit [Member] | $150 Million Term Loan Facility due July 2019 [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Variable rate (percent)		1.15%	1.15%
Kilroy Realty, L.P. [Member] | Line of Credit [Member] | $39 Million Unsecured Term Loan due July 2019 [Member]
Line of Credit Facility [Line Items]
Unsecured debt		$ 39,000
Unamortized deferred financing costs		$ 200	$ 200
Kilroy Realty, L.P. [Member] | Line of Credit [Member] | $39 Million Unsecured Term Loan due July 2019 [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Variable rate (percent)		1.15%

[1] As of March 31, 2016 and December 31, 2015, $0.9 million of unamortized deferred financing costs remained to be amortized through the maturity date of our unsecured term loan facility.

[2] Our unsecured term loan facility interest rate was calculated based on an annual rate of LIBOR plus 1.150% as of March 31, 2016 and December 31, 2015.