Secured and Unsecured Debt of the Operating Partnership - Exchangeable Senior Notes (Details Textuals) (USD $)	12 Months Ended							3 Months Ended		12 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]	Dec. 31, 2010 Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] D	Dec. 31, 2012 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] Exchangeable Note Two [Member] D		Dec. 31, 2012 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] Exchangeable Note Two [Member]		Dec. 31, 2012 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] Exchangeable Note One [Member] D	Dec. 31, 2010 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] Exchangeable Note One [Member]	Dec. 31, 2011 Kilroy Realty, L.P. [Member] Exchangeable Notes [Member] Exchangeable Note One [Member]
Debt Instrument [Line Items]
Minimum percentage of exchange price								130.00%
Minimum number of trading days closing per share price is higher than exchange price								20
Number of consecutive days trading price is less than product of closing price and exchange rate							5
Number of consecutive trading days							5
Exchangeable Notes principal amount for conversion ratio							$ 1,000
Percent of the product of the closing sale price of the common stock multiplied by the applicable exchange rate							98.00%
Number of days the Company's common stock ceases to be listed or approved for quotation							30
Number of trading days used for calculation of shares of common stock delivered for settlement												30
Exchange price, as adjusted										$ 35.93	[1]
Exchangeable note repurchased prinicipal amount													150,000,000
Repayments of Convertible Debt	148,000,000	0	0	148,000,000	0	0							151,100,000
Loss on early extinguishment of debt	0	0	4,564,000	0	0	4,564,000							4,600,000
Allocation to the equity component of cash paid upon repurchase of 3.25% Exchangeable Notes			$ 2,694,000			$ 2,694,000							$ 2,700,000
Referenced Shares Of Common Stock Under Capped Call Options								4,800,796	[2]	4,800,796	[2]			1,121,201
Exchange price including effect of capped calls								$ 42.81	[2]	$ 42.81	[2]			$ 102.72

[1] The exchange rate, exchange price, and the number of shares to be delivered upon conversion are subject to adjustment under certain circumstances including increases in our common dividends.

[2] The capped calls mitigate the dilutive impact to us of the potential exchange of all of the 4.25% Exchangeable Notes into shares of common stock.