Secured and Unsecured Debt of the Operating Partnership (Details 4) (USD $)	3 Months Ended			12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Dec. 31, 2012
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Repayments of Secured Debt	$ 84,918,000		$ 1,546,000
Unsecured debt	1,430,880,000			1,130,895,000
Kilroy Realty, L.P. [Member]
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Repayments of Secured Debt	84,918,000		1,546,000
Unsecured debt	1,430,880,000			1,130,895,000
Kilroy Realty, L.P. [Member] | Revolving Credit Facility [Member]
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Basis spread on variable rate debt	1.45%			1.45%
Debt Issuance Cost	10,200,000
Unsecured debt additional borrowing amount	200,000,000			200,000,000
Kilroy Realty, L.P. [Member] | 5.09% Mortgage Payable due August 7, 2015 [Member] | Secured Debt [Member]
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Maturity Date	Aug. 07, 2015	[1]		Aug. 07, 2015	[1]
Effective interest rate	3.50%	[1],[2],[3]		3.50%	[1],[2],[3]
Stated coupon rate	5.09%	[1],[2]		5.09%	[1],[2]
Kilroy Realty, L.P. [Member] | 4.48% Mortgage Payable due July 1, 2027 [Member] | Secured Debt [Member]
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Maturity Date	Jul. 01, 2027	[1]		Jul. 01, 2027	[1]
Effective interest rate	4.48%	[1],[2],[3]		4.48%	[1],[2],[3]
Stated coupon rate	4.48%	[1],[2]		4.48%	[1],[2]
Kilroy Realty, L.P. [Member] | 4.25% Exchangeable Notes [Member] | Exchangeable Notes [Member]
Debt Instrument [Line Items]
Referenced Shares Of Common Stock Under Capped Call Options	4,800,796			4,800,796
Exchange price including effect of capped calls	$ 42.81			$ 42.81
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Maturity Date	Nov. 15, 2014			Nov. 15, 2014
Effective interest rate	7.13%	[4]		7.13%
Exchange price, as adjusted	$ 35.93	[5]		$ 35.93
Fair value of the shares upon conversion if Exchangeable Notes were converted on specified date	247,300,000		208,700,000
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	74,800,000		36,200,000
Stated coupon rate	4.25%	[6]		4.25%	[6]
Debt Instrument, Unamortized Discount	7,478,000			8,556,000
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes, 3 Point 8 Percent, Due 2023 [Member] | Senior Notes [Member]
Secured and Unsecured Debt of the Operating Partnership (Textuals) (Abstract)
Maturity Date	Jan. 15, 2023
Unsecured debt	300,000,000
Stated coupon rate	3.80%
Debt Instrument, Unamortized Discount	$ 100,000

[1] The secured debt and the related properties that secure the debt are held in a special purpose entity and the properties are not available to satisfy the debts and other obligations of the Company or the Operating Partnership.

[2] All interest rates presented are fixed-rate interest rates.

[3] This represents the rate at which interest expense is recorded for financial reporting purposes, which reflects the amortization of discounts/premiums, excluding debt issuance costs.

[4] The rate at which we record interest expense for financial reporting purposes, which reflects the amortization of the discounts on the 4.25% 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] Interest on the 4.25% Exchangeable Notes is payable semi-annually in arrears on May 15th and November 15th of each year.