CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue, Product and Service [Extensible List]	Service [Member]	Service [Member]
REVENUES
Rental income (Note 10)	$ 230,720	$ 227,122	$ 689,849	$ 664,111
Other property income	1,606	1,192	4,106	4,954
Total revenues	232,326	228,314	693,955	669,065
EXPENSES
Property expenses	40,842	39,236	120,183	116,048
Real estate taxes	24,153	23,868	71,528	67,924
Ground leases (Notes 2 and 11)	1,708	2,119	5,559	6,766
General and administrative expenses (Note 9)	22,990	18,572	69,482	76,179
Leasing costs	798	986	2,373	3,772
Depreciation and amortization	73,213	71,863	222,734	226,318
Total expenses	163,704	156,644	491,859	497,007
OTHER INCOME (EXPENSES)
Interest income and other net investment gain (Note 12)	976	1,869	3,686	1,579
Interest expense (Note 5)	(16,105)	(19,468)	(59,829)	(49,796)
Gain on sale of depreciable operating property (Note 3)	0	0	457,831	0
Total other (expenses) income	(15,129)	(17,599)	401,688	(48,217)
NET INCOME	53,493	54,071	603,784	123,841
Net income attributable to noncontrolling common units of the Operating Partnership	(460)	(785)	(5,700)	(1,857)
Net income attributable to noncontrolling interests in consolidated property partnerships	(6,005)	(4,258)	(17,586)	(13,521)
Total income attributable to noncontrolling interests	(6,465)	(5,043)	(23,286)	(15,378)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS (UNITHOLDERS)	$ 47,028	$ 49,028	$ 580,498	$ 108,463
Net income available to common stockholders per share – basic (in dollars per share)	$ 0.40	$ 0.42	$ 4.98	$ 0.95
Net income available to common stockholders per share – diluted (in dollars per share)	$ 0.40	$ 0.42	$ 4.96	$ 0.95
Weighted average common shares outstanding – basic (in shares)	116,456,796	115,226,324	116,418,113	112,405,817
Weighted average common shares outstanding – diluted (in shares)	116,962,680	115,667,657	116,894,434	112,875,875
Kilroy Realty L.P. [Member]
Revenue, Product and Service [Extensible List]	Service [Member]	Service [Member]
REVENUES
Rental income (Note 10)	$ 230,720	$ 227,122	$ 689,849	$ 664,111
Other property income	1,606	1,192	4,106	4,954
Total revenues	232,326	228,314	693,955	669,065
EXPENSES
Property expenses	40,842	39,236	120,183	116,048
Real estate taxes	24,153	23,868	71,528	67,924
Ground leases (Notes 2 and 11)	1,708	2,119	5,559	6,766
General and administrative expenses (Note 9)	22,990	18,572	69,482	76,179
Leasing costs	798	986	2,373	3,772
Depreciation and amortization	73,213	71,863	222,734	226,318
Total expenses	163,704	156,644	491,859	497,007
OTHER INCOME (EXPENSES)
Interest income and other net investment gain (Note 12)	976	1,869	3,686	1,579
Interest expense (Note 5)	(16,105)	(19,468)	(59,829)	(49,796)
Gain on sale of depreciable operating property (Note 3)	0	0	457,831	0
Total other (expenses) income	(15,129)	(17,599)	401,688	(48,217)
NET INCOME	53,493	54,071	603,784	123,841
Total income attributable to noncontrolling interests	(6,005)	(4,343)	(17,586)	(13,886)
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS (UNITHOLDERS)	$ 47,488	$ 49,728	$ 586,198	$ 109,955
Net income available to common stockholders per share – basic (in dollars per share)	$ 0.40	$ 0.42	$ 4.98	$ 0.95
Net income available to common stockholders per share – diluted (in dollars per share)	$ 0.40	$ 0.42	$ 4.96	$ 0.94
Weighted average common shares outstanding – basic (in shares)	117,607,370	117,158,160	117,568,687	114,394,706
Weighted average common shares outstanding – diluted (in shares)	118,113,254	117,599,493	118,045,008	114,864,764