Partners' Capital of the Operating Partnership (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Partners Capital of the Operating Partnership [Abstract]
Issuance of Series G Preferred units (Note 9)	$ 96,155
Net proceeds from issuance of common stock	382,063	0
Common units held by limited partners	1,718,131	1,723,131	1,718,131
Common Stock [Member]
Partners Capital of the Operating Partnership [Abstract]
Issuance of common stock, shares	9,487,500
Kilroy Realty, L.P. [Member]
Partners Capital of the Operating Partnership [Abstract]
Issuance of Series G Preferred units (Note 9)	96,155
Common units held by general partner	68,349,843	52,419,393	58,819,717
Common general partnership interest in operating partnership	97.50%	96.80%	97.20%
Common limited partnership interest in the operating partnership	2.50%	3.20%	2.80%
Common units held by limited partners	1,718,131	1,723,131	1,718,131
Kilroy Realty, L.P. [Member] | Partners Capital Common Unit [Member]
Partners Capital of the Operating Partnership [Abstract]
Issuance of common units, units (Note 9)	9,487,500
Series G Cumulative Redeemable Preferred Stock [Member]
Partners Capital of the Operating Partnership [Abstract]
Preferred Stock, Shares Issued	4,000,000		0
Preferred stock dividend rate percentage	6.875%
Issuance of Series G Preferred units (Note 9)	96,155
Preferred Stock, Shares Outstanding	4,000,000		0
Series G Cumulative Redeemable Preferred Unit [Member] | Kilroy Realty, L.P. [Member]
Partners Capital of the Operating Partnership [Abstract]
Preferred stock dividend rate percentage	6.875%
Issuance of Series G Preferred units (Note 9)	$ 96,155
Preferred Units, Issued	4,000,000		0
Series E Cumulative Redeemable Preferred Unit [Member] | Kilroy Realty, L.P. [Member]
Partners Capital of the Operating Partnership [Abstract]
Preferred stock dividend rate percentage	7.80%		7.80%
Preferred Units, Issued	1,610,000		1,610,000
Series F Cumulative Redeemable Preferred Unit [Member] | Kilroy Realty, L.P. [Member]
Partners Capital of the Operating Partnership [Abstract]
Preferred stock dividend rate percentage	7.50%		7.50%
Preferred Units, Issued	3,450,000		3,450,000
Series E Cumulative Redeemable Preferred Stock [Member]
Partners Capital of the Operating Partnership [Abstract]
Preferred Stock, Shares Issued	1,610,000		1,610,000
Preferred stock dividend rate percentage	7.80%		7.80%
Preferred Stock, Shares Outstanding	1,610,000		1,610,000
Series F Cumulative Redeemable Preferred Stock [Member]
Partners Capital of the Operating Partnership [Abstract]
Preferred Stock, Shares Issued	3,450,000		3,450,000
Preferred stock dividend rate percentage	7.50%		7.50%
Preferred Stock, Shares Outstanding	3,450,000		3,450,000
Issuance of Equity [Member] | Common Stock [Member]
Partners Capital of the Operating Partnership [Abstract]
Issuance of common stock, shares	9,487,500
Issuance of Equity [Member] | Kilroy Realty, L.P. [Member] | Partners Capital Common Unit [Member]
Partners Capital of the Operating Partnership [Abstract]
Issuance of common units, units (Note 9)	9,487,500