Partners' Capital of the Operating Partnership (Details) (USD $)	9 Months Ended						0 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Kilroy Realty, L.P. [Member] Capital Units [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member] Capital Units [Member]	Sep. 30, 2012 Kilroy Realty, L.P. [Member] Capital Units [Member]	Sep. 18, 2013 Issuance of Equity - equity offering [Domain] Common Stock [Member]	Sep. 18, 2013 Capital Units [Member]	Sep. 30, 2013 Issuance of Equity - at the market ofering [Member] Common Stock [Member]	Sep. 30, 2013 Issuance of Equity - at the market ofering [Member] Common Stock [Member]	Sep. 30, 2013 Issuance of Equity - at the market ofering [Member] Capital Units [Member]	Sep. 30, 2013 Issuance of Equity - at the market ofering [Member] Capital Units [Member]
General Partners' Capital Account [Abstract]
Issuance of common stock, shares							6,175,000		226,430	1,040,838
Proceeds from Issuance of Common stock, net							$ 295,900,000		$ 11,400,000	$ 54,400,000
Net proceeds from issuance of common stock	$ 349,951,000	$ 662,371,000							$ 11,600,000	$ 55,300,000
Partners' Capital Account, Units, Sold in Public Offering								6,175,000			226,430	1,040,838
General Partners' Capital Account, Units Outstanding				82,113,491	74,926,981	74,692,939
Noncontrolling Interest, Ownership Percentage by Parent	97.80%	97.60%	97.60%
Common units held by limited partners	1,821,503	1,826,503	1,826,503
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	2.20%	2.40%	2.40%