Secured and Unsecured Debt of the Operating Partnership (Details 1) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Debt Instrument [Line Items]
Unsecured debt	$ 1,431,048,000			$ 1,431,048,000				$ 1,130,895,000
Balance and significant terms of the Exchangeable Notes outstanding
Net carrying amount of liability component	167,236,000			167,236,000				163,944,000
Per Share Average Trading Price Of Companys Common Stock On Stock Exchange Abstract
Average trading price of the Companys stock	$ 51.57		$ 47.56	$ 52.42		$ 45.74
Kilroy Realty, L.P. [Member]
Debt Instrument [Line Items]
Unsecured debt	1,431,048,000			1,431,048,000				1,130,895,000
Balance and significant terms of the Exchangeable Notes outstanding
Net carrying amount of liability component	167,236,000			167,236,000				163,944,000
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 6.05% Mortgage Payable Due June 1, 2019 [Member]
Balance and significant terms of the Exchangeable Notes outstanding
Maturity Date				Jun. 01, 2019
Stated coupon rate	6.05%	[1]		6.05%	[1]
Effective interest rate	3.50%	[1],[2]		3.50%	[1],[2]
Kilroy Realty, L.P. [Member] | Exchangeable Notes [Member]
Interest Expense for the Exchangeable Notes
Contractual interest payments	1,833,000		1,833,000	5,498,000		6,888,000	[3]
Amortization of discount	1,116,000		1,041,000	3,291,000		3,993,000	[3]
Interest expense attributable to the Exchangeable Notes	2,949,000		2,874,000	8,789,000		10,881,000	[3]
Kilroy Realty, L.P. [Member] | Exchangeable Notes [Member] | 4.25% Exchangeable Notes [Member]
Balance and significant terms of the Exchangeable Notes outstanding
Principal amount	172,500,000		172,500,000	172,500,000		172,500,000		172,500,000
Unamortized discount	(5,264,000)			(5,264,000)				(8,556,000)
Net carrying amount of liability component	167,236,000			167,236,000				163,944,000
Carrying amount of equity component	19,835,000			19,835,000
Stated coupon rate	4.25%	[4]		4.25%	[4]
Effective interest rate	7.13%	[5]		7.13%	[5]
Exchange rate per $1,000 principal value of the Exchangeable Notes, as adjusted	27.8307	[6]
Exchange price, as adjusted	$ 35.93	[6]
Number of Shares on which aggregate consideration to be delivered upon conversion is determined	4,800,796	[6]
Minimum percentage of exchange price	130.00%
Per Share Average Trading Price Of Companys Common Stock On Stock Exchange Abstract
Fair Value Of Shares Upon Conversion If Exchangeable Notes Were Converted On Specified Date	245,200,000		225,100,000	248,000,000		218,600,000
Debt Instrument, Convertible, If-converted Value in Excess of Principal	72,700,000		52,600,000	75,500,000		46,100,000
Capped call transactions
Referenced shares of common stock	4,800,796			4,800,796
Exchange price including effect of capped calls	$ 42.81			$ 42.81

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

[2] 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.

[3] The Company repaid the 3.25% Exchangeable Notes in April 2012. Interest payments and discount amortization for the three and nine months ended September 30, 2013 and three months ended September 30, 2012 are solely attributable to the 4.25% Exchangeable Notes.

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

[5] 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.

[6] 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.