Partners' Capital of the Operating Partnership (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Partners Capital of the Operating Partnership [Abstract]
Net proceeds from issuance of common stock	23,395	382,063
Common units held by limited partners	1,826,503	1,718,131	1,826,503
Kilroy Realty, L.P. [Member]
Partners Capital of the Operating Partnership [Abstract]
Common units held by general partner	75,349,705	68,349,843	74,926,981
Common general partnership interest in operating partnership	97.60%	97.50%	97.60%
Common limited partnership interest in the operating partnership	2.40%	2.50%	2.40%
Common units held by limited partners	1,826,503	1,718,131	1,826,503
Issuance of Equity under ATM Program [Member]
Partners Capital of the Operating Partnership [Abstract]
Issuance of common stock, shares	453,679
Net proceeds from issuance of common stock	23,400
Issuance of Equity under ATM Program [Member] | Partners Capital Common Unit [Member] | Kilroy Realty, L.P. [Member]
Partners Capital of the Operating Partnership [Abstract]
Issuance of common units	453,679