Secured and Unsecured Debt of the Operating Partnership Secured and Unsecured Debt of the Operating Partnership (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Debt Instrument [Line Items]
Net carrying amount	$ 1,130,895		$ 980,569
Kilroy Realty, L.P. [Member]
Debt Instrument [Line Items]
Net carrying amount	1,130,895		980,569
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes [Member] | 4.80% Unsecured Senior Notes due July 15, 2018 [Member]
Debt Instrument [Line Items]
Principal amount	325,000		325,000
Unamortized discount	(413)		(486)
Net carrying amount	324,587		324,514
Maturity date	Jul. 15, 2018
Stated interest rate	4.80%	[1]
Effective interest rate	4.827%	[2]
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes [Member] | 6.625% Unsecured Senior Notes due June 1, 2020 [Member]
Debt Instrument [Line Items]
Principal amount	250,000		250,000
Unamortized discount	(1,580)		(1,793)
Net carrying amount	248,420		248,207
Maturity date	Jun. 01, 2020
Stated interest rate	6.625%	[3]
Effective interest rate	6.743%	[2]
Kilroy Realty, L.P. [Member] | Unsecured Senior Notes [Member] | 5.00% Unsecured Senior Notes due Nov 3, 2015 [Member]
Debt Instrument [Line Items]
Principal amount	325,000		325,000
Unamortized discount	(112)		(152)
Net carrying amount	$ 324,888		$ 324,848
Maturity date	Nov. 03, 2015
Stated interest rate	5.00%	[4]
Effective interest rate	5.014%	[2]

[1] Interest on the 4.800% unsecured senior notes is payable semi-annually in arrears on January 15th and July 15th of each year.

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

[3] Interest on the 6.625% unsecured senior notes is payable semi-annually in arrears on June 1st and December 1st of each year.

[4] Interest on the 5.000% unsecured senior notes is payable semi-annually in arrears on May 3rd and November 3rd of each year.