Supplemental Cash Flow Information of the Operating Partnership - Supplemental Cash Flow (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $75,852, $77,666, and $65,627 as of December 31, 2020, 2019 and 2018, respectively	$ 61,741	$ 43,607	$ 44,697
Capitalized interest	75,852	77,666	65,627
Cash paid for amounts included in the measurement of ground lease liabilities	5,744	5,224
Cash paid for amounts included in the measurement of ground lease liabilities			4,398
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development properties	189,161	162,654	158,626
Tenant improvements funded directly by tenants	11,592	10,268	13,968
Assumption of accrued liabilities in connection with acquisitions (Note 3)	0	10,267	40,624
Initial measurement of operating right of use ground lease assets (Notes 2, 3 and 18)	95,523	96,348		$ 96,272
Initial measurement of operating ground lease liabilities (Notes 2, 3 and 18)	97,778	98,400		98,349
NON-CASH FINANCING TRANSACTIONS:
Accrual of distributions payable to common unitholders (Notes 14 and 27)	59,431	53,219	47,559
Kilroy Realty L.P. [Member]
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $75,852, $77,666, and $65,627 as of December 31, 2020, 2019 and 2018, respectively	61,741	43,607	44,697
Capitalized interest	75,852	77,666	65,627
Cash paid for amounts included in the measurement of ground lease liabilities	5,744	5,224
Cash paid for amounts included in the measurement of ground lease liabilities			4,398
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development properties	189,161	162,654	158,626
Tenant improvements funded directly by tenants	11,592	10,268	13,968
Assumption of accrued liabilities in connection with acquisitions (Note 3)	0	10,267	40,624
Initial measurement of operating right of use ground lease assets (Notes 2, 3 and 18)	95,523	96,348		96,272
Initial measurement of operating ground lease liabilities (Notes 2, 3 and 18)	97,778	98,400		$ 98,349
NON-CASH FINANCING TRANSACTIONS:
Accrual of distributions payable to common unitholders (Notes 14 and 27)	$ 59,431	$ 53,219	$ 47,559