CONSOLIDATED STATEMENTS OF CAPITAL (KILROY REALTY, L.P.) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 83,452	$ 45,418	$ 77,922	$ 41,794	$ 207,293	$ 215,229	$ 277,926
Non-cash amortization of share-based compensation					37,624	32,813	35,890
Settlement of restricted stock units					0	0	0
Distributions to noncontrolling interests in consolidated property partnerships					(15,247)	(12,952)	$ (11,803)
Accounting Standards Update [Extensible List]							us-gaap:AccountingStandardsUpdate201602Member
Noncontrolling Interest In Consolidated Subsidiaries [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income					20,188	19,786	$ 19,511
Distributions to noncontrolling interests in consolidated property partnerships					(15,247)	(12,952)	(11,803)
Kilroy Realty L.P. [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		4,570,858		4,201,261	4,570,858	4,201,261	3,960,316
Net income	83,452	45,418	77,922	41,794	207,293	215,229	277,926
Issuance of common units					721,665	353,722	130,693
Issuance of share-based compensation awards					4,441	4,664	3,926
Non-cash amortization of share-based compensation					37,624	32,813	35,890
Exercise of stock options						703	41
Settlement of restricted stock units					0	0	0
Repurchase of common units and restricted stock units					(14,082)	(14,861)	(16,553)
Contributions from noncontrolling interest in consolidated property partnerships							8,273
Distributions to noncontrolling interests in consolidated property partnerships					(15,247)	(12,952)	(11,803)
Distributions declared per common unit					(235,231)	(206,575)	(187,448)
Ending balance	5,277,321		4,570,858		5,277,321	4,570,858	4,201,261
Kilroy Realty L.P. [Member] | Partners Capital Common Unit [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		$ 4,369,758		$ 4,003,700	$ 4,369,758	$ 4,003,700	$ 3,773,941
Beginning balance (in units)		108,039,574		102,772,275	108,039,574	102,772,275	100,697,526
Net income					$ 189,609	$ 198,738	$ 263,210
Issuance of common units					$ 721,665	$ 353,722	$ 130,693
Issuance of common units (in units)					8,897,110	5,000,000	1,817,195
Issuance of share-based compensation awards					$ 4,441	$ 4,664	$ 3,926
Non-cash amortization of share-based compensation					$ 37,624	32,813	35,890
Exercise of stock options						$ 703	$ 41
Exercise of stock options (in units)						16,500	1,000
Settlement of restricted stock units (in units)					441,416	463,276	488,354
Repurchase of common units and restricted stock units					$ (14,082)	$ (14,861)	$ (16,553)
Repurchase of common units and restricted stock units (in units)					(191,699)	(212,477)	(231,800)
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests					$ 6,034
Distributions declared per common unit					(235,231)	$ (206,575)	$ (187,448)
Ending balance	$ 5,079,818		$ 4,369,758		$ 5,079,818	$ 4,369,758	$ 4,003,700
Ending balance (in units)	117,186,401		108,039,574		117,186,401	108,039,574	102,772,275
Kilroy Realty L.P. [Member] | Noncontrolling Interest In Consolidated Subsidiaries [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		$ 201,100		$ 197,561	$ 201,100	$ 197,561	$ 186,375
Net income					17,684	16,491	14,716
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests					(6,034)
Contributions from noncontrolling interest in consolidated property partnerships							8,273
Distributions to noncontrolling interests in consolidated property partnerships					(15,247)	(12,952)	(11,803)
Ending balance	$ 197,503		$ 201,100		$ 197,503	201,100	197,561
Cumulative Effect, Period of Adoption, Adjustment [Member] | Kilroy Realty L.P. [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				(3,146)		(3,146)
Ending balance							(3,146)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Kilroy Realty L.P. [Member] | Partners Capital Common Unit [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				$ (3,146)		$ (3,146)
Ending balance							$ (3,146)