Noncontrolling Interests on the Company's Consolidated Financial Statements (Details) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended			9 Months Ended	12 Months Ended	0 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 NumberofTradingDays	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Series A Preferred Units [Member]	Sep. 30, 2011 Series A Preferred Units [Member]	Sep. 30, 2012 Series A Preferred Units [Member]	Sep. 30, 2011 Series A Preferred Units [Member]	Dec. 31, 2011 Series A Preferred Units [Member]	Sep. 30, 2012 Kilroy Realty, L.P. [Member]	Sep. 30, 2011 Kilroy Realty, L.P. [Member]	Sep. 30, 2012 Kilroy Realty, L.P. [Member]	Sep. 30, 2011 Kilroy Realty, L.P. [Member]	Dec. 31, 2011 Kilroy Realty, L.P. [Member]	Sep. 30, 2012 Kilroy Realty, L.P. [Member] Series A Preferred Units [Member]	Dec. 31, 2011 Kilroy Realty, L.P. [Member] Series A Preferred Units [Member]	Jul. 31, 2012 6255 Sunset Boulevard, Los Angeles, CA [Member] Kilroy Realty, L.P. [Member]
Temporary Equity [Line Items]
7.45% Series A cumulative redeemable preferred units of the Operating Partnership outstanding						1,500,000		1,500,000		1,500,000
Preferred stock dividend rate percentage																	7.45%
Preferred units redemption value per unit						$ 50.00		$ 50.00		$ 50.00
Temporary Equity, Redemption Value						$ 75,000,000		$ 75,000,000
Original issuance costs of redeemed preferred stock	2,062,000	0	6,980,000	0		2,100,000		(2,062,000)			2,062,000	0	6,980,000	0		(2,062,000)
Changes to noncontrolling interest						0	0		0
Noncontrolling Interest (Textuals) [Abstract]
Percentage of general partnership interest owned by the company in the Operating Partnership	97.60%	97.10%	97.60%	97.10%	97.20%
Percentage of Common limited partnership interest owned by certain non-affiliated investors and certain directors and officers of the Company in the Operating Partnership	2.40%	2.90%	2.40%	2.90%	2.80%
Common units outstanding held by common limited partners	1,826,503	1,718,131	1,826,503	1,718,131	1,718,131						1,826,503	1,718,131	1,826,503	1,718,131	1,718,131
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares																		118,372
Conversion ratio of common units for common stock			1.0
Common stock, par value	$ 0.01		$ 0.01		$ 0.01
Number of trading days			10
Aggregate value upon redemption of outstanding noncontrolling common units	$ 84,400,000		$ 84,400,000		$ 64,700,000