Secured and Unsecured Debt of the Operating Partnership (Details 2) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2012		Dec. 31, 2011
Terms of the Credit Facility
Credit Facility	$ 27,000		$ 182,000
Kilroy Realty, L.P. [Member]
Terms of the Credit Facility
Credit Facility	27,000		182,000
Kilroy Realty, L.P. [Member] | Revolving Credit Facility [Member]
Terms of the Credit Facility
Credit Facility	27,000		182,000
Remaining borrowing capacity	473,000		318,000
Total borrowing capacity	$ 500,000	[1]	$ 500,000	[1]
Interest rate	1.97%	[2]	2.05%	[2]
Facility fee - annual rate	0.35%	[3]	0.35%
Maturity date	Aug. 10, 2015	[4]
Kilroy Realty, L.P. [Member] | Line of Credit [Member]
Terms of the Credit Facility
Maturity date			Aug. 10, 2015

[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 Credit Facility.

[2] The Credit Facility interest rate was calculated based on an annual rate of LIBOR plus 1.750% as of both September 30, 2012 and December 31, 2011.

[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 origination and legal costs of approximately $8.3 million that are currently being amortized through the maturity date of the Credit Facility.

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