Preferred and Common Units of the Operating Partnership (Details Textuals) (USD $)	12 Months Ended					1 Months Ended	12 Months Ended				12 Months Ended		12 Months Ended		1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended		12 Months Ended			0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended									1 Months Ended												0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Kilroy Realty, L.P. [Member]	Dec. 31, 2011 Kilroy Realty, L.P. [Member]	Aug. 31, 2012 Series H Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series H Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series H Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series E Cumulative Redeemable Preferred Unit [Member] Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Series E Cumulative Redeemable Preferred Unit [Member] Kilroy Realty, L.P. [Member]	Dec. 31, 2011 Series F Cumulative Redeemable Preferred Unit [Member] Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Series F Cumulative Redeemable Preferred Unit [Member] Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Series H Cumulative Redeemable Preferred Unit [Member] Kilroy Realty, L.P. [Member]	Aug. 31, 2012 Series H Cumulative Redeemable Preferred Unit [Member] Kilroy Realty, L.P. [Member]	Mar. 31, 2012 Series G Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series G Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series G Cumulative Redeemable Preferred Stock [Member]	Mar. 31, 2012 Series G Cumulative Redeemable Preferred Unit [Member] Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Series G Cumulative Redeemable Preferred Unit [Member] Kilroy Realty, L.P. [Member]	Aug. 15, 2012 Series A Preferred Units [Member]	Dec. 31, 2011 Series A Preferred Units [Member] Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Series A Preferred Units [Member] Kilroy Realty, L.P. [Member]	Dec. 31, 2010 Series A Preferred Units [Member] Kilroy Realty, L.P. [Member]	Apr. 16, 2012 Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series E Cumulative Redeemable Preferred Stock [Member]	Apr. 16, 2012 Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2010 Common Stock [Member]	Dec. 31, 2012 Issuance of Equity under ATM Program [Member]	Dec. 31, 2011 Issuance of Equity under ATM Program [Member]	Dec. 31, 2012 Issuance of Equity under ATM Program [Member] Common Stock [Member]	Dec. 31, 2011 Issuance of Equity under ATM Program [Member] Common Stock [Member]	Dec. 31, 2012 Issuance of Equity under ATM Program [Member] Partners Capital Common Unit [Member] Kilroy Realty, L.P. [Member]	Dec. 31, 2011 Issuance of Equity under ATM Program [Member] Partners Capital Common Unit [Member] Kilroy Realty, L.P. [Member]	Aug. 31, 2012 Issuance of Equity [Member]	Feb. 28, 2012 Issuance of Equity [Member]	Apr. 30, 2011 Issuance of Equity [Member]	Apr. 30, 2010 Issuance of Equity [Member]	Aug. 31, 2012 Issuance of Equity [Member] Common Stock [Member]	Feb. 28, 2012 Issuance of Equity [Member] Common Stock [Member]	Apr. 30, 2011 Issuance of Equity [Member] Common Stock [Member]	Apr. 30, 2010 Issuance of Equity [Member] Common Stock [Member]	Aug. 31, 2012 Issuance of Equity [Member] Partners Capital Common Unit [Member] Kilroy Realty, L.P. [Member]	Feb. 28, 2012 Issuance of Equity [Member] Partners Capital Common Unit [Member] Kilroy Realty, L.P. [Member]	Apr. 30, 2011 Issuance of Equity [Member] Partners Capital Common Unit [Member] Kilroy Realty, L.P. [Member]	Apr. 30, 2010 Issuance of Equity [Member] Partners Capital Common Unit [Member] Kilroy Realty, L.P. [Member]	Jul. 31, 2012 6255 Sunset Boulevard, Los Angeles, CA [Member] Kilroy Realty, L.P. [Member]
Class of Stock [Line Items]
Issuance of common units in connection with an operating property acquisition	118,372																																																118,372
Temporary Equity, Shares Outstanding																				1,500,000
Preferred stock, dividend rate						6.375%	6.375%		7.80%		7.50%		6.375%		6.875%	6.875%			6.875%		7.45%			7.80%		7.80%	7.50%		7.50%
Preferred stock issued (in shares)						4,000,000	4,000,000								4,000,000	4,000,000						1,510,000	1,510,000			1,610,000			3,450,000
Preferred units issued									1,610,000		3,450,000		4,000,000	4,000,000				4,000,000	4,000,000
Issuance of common stock, shares																														9,200,000			787,118	355,305							5,750,000	9,487,500	6,037,500	9,200,000	5,750,000	9,487,500
Net proceeds from issuance of common stock	$ 672,102,000	$ 233,312,000	$ 299,847,000																												$ 36,300,000	$ 12,800,000					$ 253,800,000	$ 382,100,000	$ 221,000,000	$ 299,800,000
Issuance of common units, units (Note 11)																																			787,118	355,305											6,037,500	9,200,000
Common units held by general partner				74,926,981	58,819,717
Common general partnership interest in operating partnership				97.60%	97.20%
Common limited partnership interest in the operating partnership				2.40%	2.80%
Common units held by limited partners	1,826,503	1,718,131		1,826,503	1,718,131
Proceeds from Issuance of Preferred Stock and Preference Stock						$ 96,200,000												$ 96,200,000
Preferred stock (in shares)							4,000,000									4,000,000					1,510,000		1,510,000	1,610,000		1,610,000	3,450,000		3,450,000
Share Price																																																	$ 47.34