Secured and Unsecured Debt of the Operating Partnership (Details Textuals) (USD $)						12 Months Ended			12 Months Ended				12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010 3.25% Exchangeable Notes [Member] Exchangeable Notes [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member]	Dec. 31, 2011 Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member] Revolving Credit Facility [Member]	Dec. 31, 2011 Kilroy Realty, L.P. [Member] Revolving Credit Facility [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member] Line of Credit [Member]		Dec. 31, 2011 Kilroy Realty, L.P. [Member] Line of Credit [Member]		Dec. 31, 2011 Kilroy Realty, L.P. [Member] 3.25% Exchangeable Notes [Member] Exchangeable Notes [Member]		Dec. 31, 2010 Kilroy Realty, L.P. [Member] 3.25% Exchangeable Notes [Member] Exchangeable Notes [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member] 3.25% Exchangeable Notes [Member] Exchangeable Notes [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member] 6.45% Unsecured Senior Notes due Aug 4 2014 [Member] Unsecured Senior Notes [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member] One Hundred Fifty Million Term Loan Facility [Member] Unsecured Term Loan [Member]
Debt Instrument [Line Items]
Fair Value Inputs, Cap Rate						6.75%	7.50%
Exchangeable note repurchased prinicipal amount															$ 150,000,000
Unsecured Debt	1,130,895,000	980,569,000		1,130,895,000	980,569,000												83,000,000	150,000,000
Effective interest rate													5.45%	[1]			6.45%
Maturity date													Apr. 15, 2012				Aug. 04, 2014	Mar. 29, 2016
Stated interest rate			3.25%					4.25%					3.25%	[2]		3.25%	6.45%
Spread on variable rate									1.45%		1.75%							1.75%
Unsecured debt additional borrowing amount									200,000,000									100,000,000
Borrowing capacity									$ 500,000,000	[3]	$ 500,000,000	[3]

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

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

[3] We may elect to borrow, subject to bank approval, up to an additional $200.0 million under an accordion feature under the terms of the revolving credit facility.