Consolidated Statements of Equity (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Total USD ($)	Common Stock [Member] USD ($)	Total Stockholders' Equity USD ($)	Preferred Stock [Member] USD ($)	Common Stock Additional Paid-in Capital USD ($)	Common Stock Distributions in Excess of Earnings USD ($)	Noncontrolling Interest [Member] USD ($)	Kilroy Realty, L.P. [Member] USD ($)	Kilroy Realty, L.P. [Member] Noncontrolling Interest [Member] USD ($)	Common Stock [Member]	Issuance of Equity under ATM Program [Member] Common Stock [Member]
Beginning Balance at Dec. 31, 2013	$ 2,516,160	$ 822	$ 2,461,312	$ 192,411	$ 2,478,975	$ (210,896)	$ 54,848
Beginning Balance, shares at Dec. 31, 2013		82,153,944
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	101,932							101,932	65
Noncash amortization of share-based compensation	2,233		2,233		2,233			2,233
Repurchase of common stock and restricted stock units, shares		(26,074)
Repurchase of common stock and restricted stock units	(1,517)		(1,517)		(1,517)
Settlement of restricted stock units for shares of common stock, shares		88,962
Settlement of restricted stock units for shares of common stock	0		0		0			0
Exercise of stock options (Note 10)		500
Exercise of stock options (Note 10)	21		21		21
Exchange of common units of the Operating Parternship, shares		1,000
Exchange of common units of the Operating Partnership	0		28		28		(28)
Preferred dividends	(3,313)		(3,313)			(3,313)		(3,313)
Dividends declared per common share and common unit ($0.35 per share/unit)	(29,906)		(29,272)			(29,272)	(634)
Ending Balance at Mar. 31, 2014	2,585,610	822	2,529,337	192,411	2,479,740	(143,636)	56,273
Ending Balance, shares at Mar. 31, 2014		82,218,332
Beginning Balance at Dec. 31, 2012
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	101,932		99,845			99,845	2,087
Ending Balance at Dec. 31, 2013	2,516,160		2,461,312	192,411		(210,896)	54,848
Beginning Balance at Dec. 31, 2014	2,723,936	863	2,666,210	192,411	2,635,900	(162,964)	57,726
Beginning Balance, shares at Dec. 31, 2014		86,259,684								86,259,684
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	44,002		43,187			43,187	815	44,002	75
Issuance of common stock, shares (Note 8)		1,507,393									1,507,393
Issuance of common stock (Note 8)	113,097	15	113,097		113,082
Issuance of share-based compensation awards, shares
Issuance of share-based compensation awards	413		413		413
Noncash amortization of share-based compensation	4,302		4,302		4,302			4,302
Repurchase of common stock and restricted stock units, shares		(20,429)
Repurchase of common stock and restricted stock units	(1,821)		(1,821)		(1,821)
Settlement of restricted stock units for shares of common stock, shares		36,699
Settlement of restricted stock units for shares of common stock	0		0		0			0
Exercise of stock options (Note 10)		237,000
Exercise of stock options (Note 10)	10,482	2	10,482		10,480
Exchange of common units of the Operating Parternship, shares		11,030
Exchange of common units of the Operating Partnership	0		316		316		(316)
Adjustment for noncontrolling interest	0		(1,496)		(1,496)		1,496
Preferred dividends	(3,313)		(3,313)			(3,313)		(3,313)
Dividends declared per common share and common unit ($0.35 per share/unit)	(31,892)		(31,265)			(31,265)	(627)
Ending Balance at Mar. 31, 2015	$ 2,859,206	$ 880	$ 2,800,112	$ 192,411	$ 2,761,176	$ (154,355)	$ 59,094
Ending Balance, shares at Mar. 31, 2015		88,031,377								88,031,377