Secured and Unsecured Debt of the Operating Partnership (Details) (USD $) In Thousands, except Share data, unless otherwise specified								9 Months Ended		12 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Sep. 30, 2011 Kilroy Realty, L.P. [Member]		Dec. 31, 2010 Kilroy Realty, L.P. [Member]	Sep. 30, 2010 Kilroy Realty, L.P. [Member]	Sep. 30, 2011 Kilroy Realty, L.P. [Member] 3.25% Exchangeable Notes [Member]		Dec. 31, 2010 Kilroy Realty, L.P. [Member] 3.25% Exchangeable Notes [Member]		Sep. 30, 2011 Kilroy Realty, L.P. [Member] 4.25% Exchangeable Notes [Member]		Dec. 31, 2010 Kilroy Realty, L.P. [Member] 4.25% Exchangeable Notes [Member]
Balance and significant terms of the Exchangeable Notes outstanding
Principal amount				$ 1,776,900	[1]			$ 148,000		$ 148,000		$ 172,500		$ 172,500
Unamortized discount								(1,714)		(4,004)		(13,671)		(16,532)
Net carrying amount of liability component	305,115	299,964		305,115		299,964		146,286		143,996		158,829		155,968
Carrying amount of equity component								$ 33,675		$ 33,675		$ 19,835		$ 19,835
Maturity Date								Apr. 15, 2012		Apr. 15, 2012		Nov. 15, 2014		Nov. 15, 2014
Stated coupon rate			3.25%				3.25%	3.25%	[2]	3.25%	[2]	4.25%	[3]	4.25%	[3]
Effective interest rate								5.45%	[4]	5.45%	[4]	7.13%	[4]	7.13%	[4]
Exchange rate per $1,000 principal value of the Exchangeable Notes, as adjusted								11.3636	[5]	11.3636	[5]	27.8307	[5]	27.8307	[5]
Exchange price, as adjusted								$ 88	[5]	$ 88	[5]	$ 35.93	[5]	$ 35.93	[5]
Number of Shares on which aggregate consideration to be delivered upon conversion is determined								1,681,813	[5]	1,681,813	[5]	4,800,796	[5]	4,800,796	[5]
Capped call transactions
Referenced shares of common stock under capped call options								1,121,201	[6]	1,121,201	[6]	4,800,796	[7]	4,800,796	[7]
Exchange price including effect of capped calls								$ 102.72	[6]	$ 102.72	[6]	$ 42.81	[7]	$ 42.81	[7]

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

[2] Interest on the 3.25% Exchangeable Notes is payable semi-annually in arrears on April 15th and October 15th of each year.

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

[4] 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.

[5] 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.

[6] The capped calls mitigate the dilutive impact to us of the potential exchange of two-thirds of the 3.25% Exchangeable Notes into shares of common stock.

[7] The capped calls mitigate the dilutive impact to us of the potential exchange of all of the 4.25% Exchangeable Notes into shares of common stock.