Secured and Unsecured Debt of the Operating Partnership (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Terms of the Credit Facility
Unsecured line of credit	$ 0		$ 185,000
Kilroy Realty, L.P. [Member]
Terms of the Credit Facility
Unsecured line of credit	0		185,000
Kilroy Realty, L.P. [Member] | Revolving Credit Facility [Member]
Terms of the Credit Facility
Unsecured line of credit	0		185,000
Remaining borrowing capacity	500,000		315,000
Total borrowing capacity	$ 500,000	[1]	$ 500,000	[1]
Interest rate	0.00%	[2]	1.66%	[2]
Facility fee - annual rate	0.30%	[3]	0.30%
Maturity date	Apr. 03, 2017	[4]	Apr. 03, 2017

[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% as of both March 31, 2013 and December 31, 2012.

[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, from 2010 to 2012 we incurred debt origination and legal costs totaling approximately $10.2 million that are currently being amortized through the maturity date of the revolving credit facility.

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