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, 2012	$ 2,235,933	$ 749	$ 2,189,630	$ 192,411	$ 2,126,005	$ (129,535)	$ 46,303
Beginning Balance, shares at Dec. 31, 2012		74,926,981
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	21,518		21,252			21,252	266	21,518	178
Issuance of common stock (Note 7), shares		7,215,838
Issuance of common stock (Note 7)	349,951	72	349,951		349,879
Issuance of share-based compensation awards, shares		0
Issuance of share-based compensation awards	1,075		1,075		1,075
Noncash amortization of share-based compensation	7,096		7,096		7,096			7,096
Repurchase of common stock and restricted stock units, shares		(34,164)
Repurchase of common stock and restricted stock units	(1,803)		(1,803)		(1,803)
Settlement of restricted stock units for shares of common stock, shares		4,363
Settlement of restricted stock units for shares of common stock	(10)		(10)		(10)			(10)
Exercise of stock options, net, shares		473
Exercise of stock options, net	128		128		128
Adjustment for noncontrolling interest	0		(5,946)		(5,946)		5,946
Contribution by noncontrolling interest in consolidated subsidiary	4,885						4,885	4,885	4,885
Preferred dividends	(9,938)		(9,938)			(9,938)		(9,938)
Dividends declared per common share and common unit ($1.05 per share/unit)	(84,741)		(82,827)			(82,827)	(1,914)
Ending Balance at Sep. 30, 2013	2,524,094	821	2,468,608	192,411	2,476,424	(201,048)	55,486
Ending Balance, shares at Sep. 30, 2013		82,113,491
Beginning Balance at Jun. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	9,027							9,027
Ending Balance at Sep. 30, 2013	2,524,094			192,411
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								82,153,944
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	152,378		149,367			149,367	3,011	152,378	201
Issuance of common stock (Note 7), shares		370,700									370,700
Issuance of common stock (Note 7)	22,136	4	22,136		22,132
Issuance of share-based compensation awards, shares		0
Issuance of share-based compensation awards	1,281		1,281		1,281
Noncash amortization of share-based compensation	10,345		10,345		10,345			10,345
Repurchase of common stock and restricted stock units, shares		(48,017)
Repurchase of common stock and restricted stock units	(2,861)		(2,861)		(2,861)
Settlement of restricted stock units for shares of common stock, shares		108,529
Settlement of restricted stock units for shares of common stock	0		0		0			0
Common shares issued in connection with early exchange of 4.25% Exchangeable Senior Notes (Note 5), shares		431,270
Common shares issued in connection with early exchange of 4.25% Exchangeable Senior Notes, net of equity component (Note 5)	223	4	223		219			223
Common shares received in connection with capped call option transactions (Note 5), shares		(111,206)
Common shares received in connection with capped call option transactions (Note 5)	0		0					0
Exercise of stock options, net, shares		482,000
Exercise of stock options, net	20,537	4	20,537		20,533
Exchange of common units of the Operating Parternship, shares		1,000
Exchange of common units of the Operating Partnership	0		28		28		(28)
Adjustment for noncontrolling interest	0		(370)		(370)		370
Contribution by noncontrolling interest in consolidated subsidiary	336						336	336	336
Preferred dividends	(9,938)		(9,938)			(9,938)		(9,938)
Dividends declared per common share and common unit ($1.05 per share/unit)	(90,228)		(88,332)			(88,332)	(1,896)
Ending Balance at Sep. 30, 2014	2,620,369	834	2,563,728	192,411	2,530,282	(159,799)	56,641
Ending Balance, shares at Sep. 30, 2014		83,388,220								83,388,220
Beginning Balance at Jun. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	19,303							19,303
Ending Balance at Sep. 30, 2014	$ 2,620,369			$ 192,411
Ending Balance, shares at Sep. 30, 2014										83,388,220