Secured and Unsecured Debt of the Operating Partnership (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Capitalized interest and loan fees
Interest expense (Note 5)		$ 79,114		$ 85,785	$ 55,082
Kilroy Realty, L.P. [Member]
Capitalized interest and loan fees
Gross interest expense	69,661	98,906		94,915
Capitalized interest	(10,015)	(19,792)		(9,130)
Interest expense (Note 5)	59,646	79,114		85,785	55,082
Debt [Member] | Kilroy Realty, L.P. [Member]
Stated debt maturities and scheduled amortization payments, excluding debt discounts
2013		90,881
2014		263,913
2015		393,711
2016		247,822
2017		255,036
Thereafter		793,056
Total		$ 2,044,419	[1]

[1] Includes gross principal balance of outstanding debt before impact of all debt discounts and premiums.