Secured and Unsecured Debt of the Operating Partnership (Details 3) (USD $)	1 Months Ended		12 Months Ended
	Nov. 30, 2012	Jun. 30, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Terms of the Credit Facility
Outstanding borrowings			$ 185,000,000		$ 182,000,000
Kilroy Realty, L.P. [Member]
Terms of the Credit Facility
Outstanding borrowings			185,000,000		182,000,000
Line of Credit [Member] | Kilroy Realty, L.P. [Member]
Terms of the Credit Facility
Outstanding borrowings			185,000,000		182,000,000
Remaining borrowing capacity			315,000,000		318,000,000
Total borrowing capacity			500,000,000	[1]	500,000,000	[1]
Interest rate			1.66%	[2]	2.05%	[2]
Facility fee - annual rate			0.30%	[3]	0.35%	[3]
Maturity date			Apr. 03, 2017	[4]	Aug. 10, 2015	[4]
Unsecured debt additional borrowing amount			200,000,000
Spread on variable rate			1.45%		1.75%
Amount Incurred In Debt Origination And Legal Costs	$ 1,900,000	$ 3,300,000					$ 5,000,000

[1] We may elect to borrow, subject to bank approval, up to an additional $200.0 million under an accordion feature under the terms of the revolving credit facility.

[2] The revolving credit facility interest rate was calculated based on an annual rate of LIBOR plus 1.450% and 1.750% as of December 31, 2012 and December 31, 2011, respectively.

[3] The facility fee is paid on a quarterly basis and is calculated based on the total borrowing capacity. In addition to the facility fee, we also incurred debt origination and legal costs of approximately $5.0 million when we entered into the revolving credit facility in 2010, an additional $3.3 million when we amended the terms of the revolving credit facility in June 2011 and an additional $1.9 million when we amended the terms of the revolving credit facility in November 2012. The unamortized balance of these costs are amortized through the extended maturity date of the revolving credit facility.

[4] Under the original and all amended terms of the revolving credit facility, we may exercise an option to extend the maturity date by one year.