Secured and Unsecured Debt of the Operating Partnership (Details 3) (USD $)	3 Months Ended			12 Months Ended
	Mar. 31, 2012		Mar. 31, 2011	Dec. 31, 2011
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Unsecured debt	$ 1,130,651,000			$ 980,569,000
Kilroy Realty, L.P. [Member]
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Unsecured debt	1,130,651,000			980,569,000
Kilroy Realty, L.P. [Member] | Line of Credit [Member]
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Unsecured debt additional borrowing amount	200,000,000
Basis spread on variable rate debt	1.75%			1.75%
Amount Incurred In Debt Origination And Legal Costs	8,300,000
Fair market value cap rate	6.75%			7.50%
Unsecured debt maturity extension	1 year			1 year
Kilroy Realty, L.P. [Member] | 3.25% Exchangeable Notes [Member] | Exchangeable Notes [Member]
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Maturity Date	Apr. 15, 2012			Apr. 15, 2012
Stated coupon rate	3.25%	[1]		3.25%	[1]
Debt discount	132,000			924,000
Debt Instrument, Interest Rate, Effective Percentage	5.45%	[2]		5.45%	[2]
Debt Instrument, Convertible, Conversion Price	$ 88	[3]		$ 88	[3]
Principal amount	148,000,000			148,000,000
Kilroy Realty, L.P. [Member] | 4.25% Exchangeable Notes [Member] | Exchangeable Notes [Member]
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Maturity Date	Nov. 15, 2014			Nov. 15, 2014
Stated coupon rate	4.25%	[4]		4.25%	[4]
Debt discount	11,679,000			12,684,000
Debt Instrument, Interest Rate, Effective Percentage	7.13%	[2]		7.13%	[2]
Debt Instrument, Convertible, Conversion Price	$ 35.93	[3]		$ 35.93	[3]
Fair value of the shares upon conversion if Exchangeable Notes were converted on specified date	208,700,000		182,500,000
Principal amount	172,500,000			172,500,000
Amount by which fair value of the shares upon conversion exceeds principal amount of the Exchangeable Notes on the specified date	36,200,000		10,000,000
Kilroy Realty, L.P. [Member] | $150M Unsecured Term Loan Facility [Member] | Unsecured Term Loan [Member]
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Maturity Date	Mar. 29, 2016
Unsecured debt	150,000,000
Unsecured debt additional borrowing amount	$ 100,000,000
Basis spread on variable rate debt	1.75%
Unsecured debt maturity extension	1 year

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

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