Consolidated Statements of Capital (KILROY REALTY, L.P.) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 38,310		$ 75,488	$ 111,036	$ 148,075
Redemption of Series G and H Preferred units					(200,000)
Non-cash amortization of share-based compensation				24,678	19,013
Exercise of stock options				0	0
Distributions to noncontrolling interests in consolidated property partnerships				(7,006)	(12,234)
Preferred distributions					(5,774)
Noncontrolling Interests [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				12,841	11,992
Distributions to noncontrolling interests in consolidated property partnerships				(7,006)	(12,234)
Kilroy Realty L.P. [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		$ 3,960,316		3,960,316	3,759,317
Net income	38,310		75,488	111,036	148,075
Redemption of Series G and H Preferred units					(200,000)
Issuance of common units				130,744	308,812
Issuance of share-based compensation awards				3,298	5,291
Non-cash amortization of share-based compensation				24,678	19,013
Exercise of stock options				41	12,051
Exercise of stock options				0	0
Repurchase of common units, stock options and restricted stock units				(16,553)	(12,986)
Contributions from noncontrolling interests in consolidated property partnerships		8,273			250
Distributions to noncontrolling interests in consolidated property partnerships				(7,006)	(12,234)
Preferred distributions					(5,774)
Distributions declared per common unit ($1.335 and $1.225 per unit for the nine months ended September 2018 and 2017, respectively)				(139,908)	(125,935)
Ending balance	4,074,919		3,895,880	4,074,919	3,895,880
Kilroy Realty L.P. [Member] | Partners Capital Preferred Units [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance					192,411
Redemption of Series G and H Preferred units					(192,411)
Ending balance			0		0
Kilroy Realty L.P. [Member] | Partners Capital Common Unit [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		$ 3,773,941		$ 3,773,941	$ 3,431,768
Beginning balance (in units)		100,697,526		100,697,526	95,600,982
Net income				$ 99,901	$ 138,427
Redemption of Series G and H Preferred units					$ (7,589)
Issuance of common units (in units)				1,817,195	4,427,500
Issuance of common units				$ 130,744	$ 308,812
Issuance of share-based compensation awards				3,298	5,291
Non-cash amortization of share-based compensation				$ 24,678	$ 19,013
Exercise of stock options (in shares)				1,000	282,000
Exercise of stock options				$ 41	$ 12,051
Settlement of restricted stock units (in units)				488,354	317,848
Exercise of stock options				$ 0	$ 0
Repurchase of common units and restricted stock units (in units)				(231,800)	(168,881)
Repurchase of common units, stock options and restricted stock units				$ (16,553)	$ (12,986)
Contributions from noncontrolling interests in consolidated property partnerships		$ 0
Preferred distributions					(5,774)
Distributions declared per common unit ($1.335 and $1.225 per unit for the nine months ended September 2018 and 2017, respectively)				(139,908)	(125,935)
Ending balance	$ 3,876,142		$ 3,763,078	$ 3,876,142	$ 3,763,078
Ending balance (in units)	102,772,275		100,459,449	102,772,275	100,459,449
Kilroy Realty L.P. [Member] | Total Partners Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance					$ 3,624,179
Net income					138,427
Redemption of Series G and H Preferred units					(200,000)
Issuance of common units					308,812
Issuance of share-based compensation awards					5,291
Non-cash amortization of share-based compensation					19,013
Exercise of stock options					12,051
Exercise of stock options					0
Repurchase of common units, stock options and restricted stock units					(12,986)
Contributions from noncontrolling interests in consolidated property partnerships
Preferred distributions					(5,774)
Distributions declared per common unit ($1.335 and $1.225 per unit for the nine months ended September 2018 and 2017, respectively)					(125,935)
Ending balance			$ 3,763,078		3,763,078
Kilroy Realty L.P. [Member] | Noncontrolling Interests [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		186,375		$ 186,375	135,138
Net income				11,135	9,648
Contributions from noncontrolling interests in consolidated property partnerships		$ 8,273			250
Distributions to noncontrolling interests in consolidated property partnerships				(7,006)	(12,234)
Ending balance	$ 198,777		$ 132,802	$ 198,777	$ 132,802