Partners' Capital of the Operating Partnership (Details) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Partners Capital of the Operating Partnership [Abstract]
Net proceeds from issuance of common stock	$ 221,015	$ 299,847
Limited partnership units outstanding	1,718,131	1,723,131	1,723,131
Kilroy Realty, L.P. [Member]
Partners Capital of the Operating Partnership [Abstract]
Common units in Operating Partnership held by the Company, the general partner	58,464,412	52,349,670	52,349,670
Common general partnership interest in operating partnership	97.10%	96.80%	96.80%
Common limited partnership interest in the operating partnership	2.90%	3.20%	3.20%
Limited partnership units outstanding	1,718,131	1,723,131	1,723,131
Kilroy Realty, L.P. [Member] | Partners Capital Common Unit [Member]
Partners Capital of the Operating Partnership [Abstract]
Issuance of common units, units (Note 8)	6,037,500	9,200,000
Common Stock [Member]
Partners Capital of the Operating Partnership [Abstract]
Underwriting public offering of common stock, shares	6,037,500	9,200,000