Unsecured Senior Notes (Details 2) (USD $) In Thousands, unless otherwise specified					9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member]	Sep. 30, 2013 Kilroy Realty, L.P. [Member] Unsecured Senior Notes, 3.8%, Due 2023 [Member] Senior Notes [Member]
Debt Instrument [Line Items]
Unsecured debt	$ 1,431,048	$ 1,130,895	$ 1,431,048	$ 1,130,895	$ 300,000
Maturity Date					Jan. 15, 2023
Stated coupon rate					3.80%
Debt Instrument, Unamortized Discount					$ 100