Secured and Unsecured Debt of the Operating Partnership (Details 3) (USD $)	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Capitalized interest and loan fees
Interest expense	$ 19,734,000		$ 21,163,000
Kilroy Realty, L.P. [Member]
Capitalized interest and loan fees
Gross interest expense	27,466,000		24,994,000
Capitalized interest	(7,732,000)		(3,831,000)
Interest expense	19,734,000		21,163,000
Debt [Member] | Kilroy Realty, L.P. [Member]
Stated debt maturities and scheduled amortization payments, excluding debt discounts
Remainder of 2013	7,016,000
2014	265,346,000
2015	395,104,000
2016	249,431,000
2017	71,748,000
Thereafter	1,169,741,000
Total	2,158,386,000	[1]
Debt Instrument, Unamortized Discount (Premium), Net	$ 8,200,000

[1] Includes gross principal balance of outstanding debt before impact of net unamortized premiums totaling approximately $8.2 million.