Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Variable Interest Entity, Consolidated, Carrying Amount, Assets	$ 135,300,000	$ 337,000,000
Common stock, par value	$ 0.01
Common Stock [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	82,113,491	74,926,981
Common stock, shares outstanding	82,113,491	74,926,981
Preferred Stock [Member]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	30,000,000	30,000,000
Series G Cumulative Redeemable Preferred Stock
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock dividend rate percentage	6.875%	6.875%
Preferred stock, shares authorized	4,600,000	4,600,000
Preferred stock, shares issued	4,000,000	4,000,000
Preferred stock, shares outstanding	4,000,000	4,000,000
Preferred Stock Liquidation preference	100,000,000	100,000,000
Series H Cumulative Redeemable Preferred Stock
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock dividend rate percentage	6.375%	6.375%
Preferred stock, shares authorized	4,000,000	4,000,000
Preferred stock, shares issued	4,000,000	4,000,000
Preferred stock, shares outstanding	4,000,000	4,000,000
Preferred Stock Liquidation preference	100,000,000	100,000,000
Real Estate Investment [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	119,262,000	319,770,000
Kilroy Realty, L.P. [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	$ 119,262,000	$ 319,770,000