Supplemental Cash Flow Information of the Operating Partnership - Supplemental Cash Flow (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $55,423 and $58,405 as of September 30, 2021 and 2020, respectively	$ 47,832	$ 35,898
Capitalized interest	55,423	58,405
Cash paid for amounts included in the measurement of ground lease liabilities	4,939	4,686
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development properties	79,891	154,253
Tenant improvements funded directly by tenants	8,179	9,118
Assumption of accrued liabilities in connection with acquisitions (Notes 2 and 11)	37,572	0
Initial measurement of operating right of use ground lease assets (Notes 2 and 11)	46,430	0
Initial measurement of operating ground lease liabilities (Notes 2 and 11)	46,430	0
NON-CASH FINANCING TRANSACTIONS:
Accrual of distributions payable to common unitholders (Note 17)	61,845	59,416
Kilroy Realty L.P. [Member]
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $55,423 and $58,405 as of September 30, 2021 and 2020, respectively	47,832	35,898
Capitalized interest	55,423	58,405
Cash paid for amounts included in the measurement of ground lease liabilities	4,939	4,686
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development properties	79,891	154,253
Tenant improvements funded directly by tenants	8,179	9,118
Assumption of accrued liabilities in connection with acquisitions (Notes 2 and 11)	37,572	0
Initial measurement of operating right of use ground lease assets (Notes 2 and 11)	46,430	0
Initial measurement of operating ground lease liabilities (Notes 2 and 11)	46,430	0
NON-CASH FINANCING TRANSACTIONS:
Accrual of distributions payable to common unitholders (Note 17)	$ 61,845	$ 59,416