Subsequent Events (Details) (USD $)	3 Months Ended				3 Months Ended				0 Months Ended				0 Months Ended								3 Months Ended	12 Months Ended	0 Months Ended		3 Months Ended	12 Months Ended	0 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2012 Kilroy Realty, L.P. [Member]	Mar. 31, 2011 Kilroy Realty, L.P. [Member]	Dec. 31, 2011 Kilroy Realty, L.P. [Member]	Dec. 31, 2010 Kilroy Realty, L.P. [Member]	Apr. 17, 2012 Cumulative Preferred Stock Subject to Mandatory Redemption [Member]	Apr. 17, 2012 Dividend Paid [Member]	Apr. 30, 2012 Acquisition [Member]	Apr. 27, 2012 Cash and Cash Equivalents [Member]	Apr. 27, 2012 Restricted cash [Member]	Apr. 27, 2012 Line of Credit [Member] Kilroy Realty, L.P. [Member]	Apr. 16, 2012 Exchangeable Notes [Member] Repayment of Debt [Member] Kilroy Realty, L.P. [Member]	Mar. 31, 2012 Exchangeable Note One [Member] Exchangeable Notes [Member] Kilroy Realty, L.P. [Member]		Dec. 31, 2011 Exchangeable Note One [Member] Exchangeable Notes [Member] Kilroy Realty, L.P. [Member]		Apr. 16, 2012 Exchangeable Note One [Member] Exchangeable Notes [Member] Repayment of Debt [Member] Kilroy Realty, L.P. [Member]	Mar. 31, 2012 Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series E Cumulative Redeemable Preferred Stock [Member]	Apr. 17, 2012 Series E Cumulative Redeemable Preferred Stock [Member] Cumulative Preferred Stock Subject to Mandatory Redemption [Member]	Apr. 16, 2012 Series E Cumulative Redeemable Preferred Stock [Member] Cumulative Preferred Stock Subject to Mandatory Redemption [Member]	Mar. 31, 2012 Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series F Cumulative Redeemable Preferred Stock [Member]	Apr. 17, 2012 Series F Cumulative Redeemable Preferred Stock [Member] Cumulative Preferred Stock Subject to Mandatory Redemption [Member]	Apr. 16, 2012 Series F Cumulative Redeemable Preferred Stock [Member] Cumulative Preferred Stock Subject to Mandatory Redemption [Member]
Subsequent Events (Textuals) [Abstract]
Stated coupon rate																3.25%	[1]	3.25%	[1]	3.25%
Principal amount															$ 148,000,000	$ 148,000,000		$ 148,000,000
Preferred Stock, Shares Outstanding																					1,610,000	1,610,000		1,610,000	3,450,000	3,450,000		3,450,000
Preferred stock dividend rate percentage																					7.80%	7.80%	7.80%		7.50%	7.50%	7.50%
Payments for Repurchase of Preferred Stock and Preference Stock									126,500,000
Aggregate dividends, distributions, and dividend equivalents paid to common stockholders and common unitholders	21,191,000	18,925,000			21,191,000	18,925,000				24,900,000
Non-refundable escrow deposits related to potential future acquisitions	10,000,000										15,000,000
Cash and cash equivalents	374,368,000	6,708,000	4,777,000	14,840,000	374,368,000	6,708,000	4,777,000	14,840,000				44,236,000
Net proceeds from disposition held by a qualified intermediary in connection wtih Section 1031 exchange	42,395,000	0			42,395,000	0							42,395,000
Credit Facility	$ 0		$ 182,000,000		$ 0		$ 182,000,000							$ 0

[1] Interest on the 3.25% Exchangeable Notes is payable semi-annually in arrears on April 15th and October 15th of each year.