Secured and Unsecured Debt of the Operating Partnership (Details 1) (USD $) In Thousands, unless otherwise specified			9 Months Ended		12 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2011 Kilroy Realty, L.P. [Member]		Dec. 31, 2010 Kilroy Realty, L.P. [Member]		Sep. 30, 2011 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member]	Sep. 30, 2010 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member]	Sep. 30, 2011 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member]	Sep. 30, 2010 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member]
Interest Expense for the Exchangeable Notes
Contractual interest payments							$ 3,035	$ 3,035	$ 9,106	$ 11,530
Amortization of discount							1,742	1,818	5,151	6,497
Interest expense attributable to the Exchangeable Notes							4,777	4,853	14,257	18,027
Terms of the Credit Facility
Credit Facility	0	159,000	0	[1]	159,000
Remaining borrowing capacity			500,000		341,000
Total borrowing capacity			$ 500,000	[2]	$ 500,000	[2]
Interest rate				[3]	2.99%	[3]
Facility fee - annual rate			0.35%	[4]	0.575%	[4]
Maturity date			August 2015	[5]	August 2013	[5]

[1] As of September 30, 2011, there were no borrowings outstanding on the Credit Facility.

[2] We may elect to borrow, subject to lender approval, up to an additional $200 million under an accordion feature under the terms of the Credit Facility.

[3] The Credit Facility interest rate was calculated based on an annual rate of LIBOR plus 1.750% and 2.675% as of September 30, 2011 and December 31, 2010, respectively. No interest rate is shown as of September 30, 2011 because no borrowings were outstanding.

[4] 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 Credit Facility in 2010 and an additional $3.3 million when we amended the Credit Facility in 2011. The unamortized balance of these costs will be amortized as additional interest expense over the extended term of the Credit Facility.

[5] Under the original and amended terms of the Credit Facility, we may exercise an option to extend the maturity date by one year.