Secured and Unsecured Debt of the Operating Partnership - Unsecured Revolving Credit Facility (Details) - USD ($)		3 Months Ended	12 Months Ended
		Mar. 31, 2016	Dec. 31, 2015
Terms of the Credit Facility
Unsecured line of credit		$ 75,000,000	$ 0
Kilroy Realty, L.P. [Member]
Terms of the Credit Facility
Unsecured line of credit		75,000,000	0
Unamortized deferred financing costs		12,500,000
Kilroy Realty, L.P. [Member] | Revolving Credit Facility [Member]
Terms of the Credit Facility
Unsecured line of credit		75,000,000	0
Remaining borrowing capacity		525,000,000	600,000,000
Total borrowing capacity	[1]	$ 600,000,000	$ 600,000,000
Interest rate (percent)	[2]	1.49%	0.00%
Facility fee-annual rate (percent)	[3]	0.20%	0.20%
Maturity date		Jul. 01, 2019	Jul. 01, 2019
Contingent additional borrowings		$ 311,000,000
Variable rate (percent)		1.05%	1.05%
Unamortized deferred financing costs		$ 4,300,000	$ 4,600,000

[1] We may elect to borrow, subject to bank approval and obtaining commitments for any additional borrowing capacity, up to an additional $311.0 million under an accordion feature under the terms of the unsecured revolving credit facility and term loan facility.

[2] Our unsecured revolving credit facility interest rate was calculated based on an annual rate of LIBOR plus 1.050% as of March 31, 2016 and December 31, 2015.

[3] Our facility fee is paid on a quarterly basis and is calculated based on the total borrowing capacity. In addition to the facility fee, we incurred debt origination and legal costs. As of March 31, 2016 and December 31, 2015, $4.3 million and $4.6 million, of unamortized deferred financing costs, respectively, remained to be amortized through the maturity date of our unsecured revolving credit facility, which are included in prepaid expenses and other assets, net on our consolidated balance sheets.