Secured and Unsecured Debt of the Operating Partnership (Details 1) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended			12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Kilroy Realty, L.P. [Member]	Dec. 31, 2011 Kilroy Realty, L.P. [Member]	Sep. 30, 2012 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member]	Sep. 30, 2011 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member]	Sep. 30, 2012 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member]	Sep. 30, 2011 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member]	Sep. 30, 2012 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] 4.25% Exchangeable Notes [Member] D		Sep. 30, 2012 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] 4.25% Exchangeable Notes [Member]		Sep. 30, 2011 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] 4.25% Exchangeable Notes [Member]	Dec. 31, 2011 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] 4.25% Exchangeable Notes [Member]	Dec. 31, 2011 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] 3.25% Exchangeable Notes [Member]		Sep. 30, 2012 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] 3.25% Exchangeable Notes [Member]
Balance and significant terms of the Exchangeable Notes outstanding
Principal amount												$ 172,500		$ 172,500			$ 172,500	$ 148,000		$ 0
Unamortized discount												(9,615)		(9,615)			(12,684)	(924)		0
Net carrying amount of liability component	162,885		162,885		306,892	162,885	306,892					162,885		162,885			159,816	147,076		0
Carrying amount of equity component												19,835		19,835			19,835	33,675
Maturity Date														Nov. 15, 2014			Nov. 15, 2014	Apr. 15, 2012
Stated coupon rate												4.25%	[1]	4.25%	[1]		4.25%	3.25%
Effective interest rate												7.13%	[2]	7.13%	[2]		7.13%	5.45%	[2]
Exchange rate per $1,000 principal value of the Exchangeable Notes, as adjusted														27.8307	[3]		27.8307
Exchange price, as adjusted														$ 35.93	[3]	$ 35.93	$ 35.93
Number of Shares on which aggregate consideration to be delivered upon conversion is determined														4,800,796	[3]		4,800,796
Minimum percentage of exchange price												130.00%
Per Share Average Trading Price Of Companys Common Stock On Stock Exchange Abstract
Average trading price of the Companys stock	$ 47.56	$ 35.93	$ 45.74	$ 37.92
Capped call transactions
Referenced shares of common stock												4,800,796		4,800,796			4,800,796	1,121,201
Exchange price including effect of capped calls												$ 42.81		$ 42.81			$ 42.81	$ 102.72
Interest Expense for the Exchangeable Notes
Contractual interest payments								1,833	3,035	6,888	9,106
Amortization of discount								1,041	1,742	3,993	5,151
Interest expense attributable to the Exchangeable Notes								$ 2,874	$ 4,777	$ 10,881	$ 14,257
Minimum number of trading days closing per share price is higher than exchange price												20

[1] Interest on the 4.25% Exchangeable Notes is payable semi-annually in arrears on May 15th and November 15th of each year.

[2] The rate at which we record interest expense for financial reporting purposes, which reflects the amortization of the discounts on the Exchangeable Notes. This rate represents our conventional debt borrowing rate at the date of issuance.

[3] The exchange rate, exchange price, and the number of shares to be delivered upon conversion are subject to adjustment under certain circumstances including increases in our common dividends.