Supplemental Cash Flow Information of the Operating Partnership - Supplemental Cash Flow (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $77,666, $65,627, and $44,757 as of December 31, 2019, 2018 and 2017, respectively	$ 43,607	$ 44,697	$ 67,336
Capitalized interest	77,666	65,627	44,757
Cash paid for amounts included in the measurement of ground lease liabilities	5,224
Cash paid for amounts included in the measurement of ground lease liabilities		4,398	4,809
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development properties	162,654	158,626	116,089
Assumption of accrued liabilities in connection with acquisitions (Note 3)	10,267	40,624	1,443
Tenant improvements funded directly by tenants	10,268	13,968	15,314
Initial measurement of operating right of use ground lease assets (Notes 2, 3 and 18)	96,348			$ 96,272
Initial measurement of operating ground lease liabilities (Notes 2, 3 and 18)	98,400			98,349
NON-CASH FINANCING TRANSACTIONS:
Accrual of dividends and distributions payable to common stockholders and common unitholders (Notes 14 and 28)	53,219	47,559	43,448
Kilroy Realty L.P. [Member]
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $77,666, $65,627, and $44,757 as of December 31, 2019, 2018 and 2017, respectively	43,607	44,697	67,336
Capitalized interest	77,666	65,627	44,757
Cash paid for amounts included in the measurement of ground lease liabilities	5,224
Cash paid for amounts included in the measurement of ground lease liabilities		4,398	4,809
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development properties	162,654	158,626	116,089
Assumption of accrued liabilities in connection with acquisitions (Note 3)	10,267	40,624	1,443
Tenant improvements funded directly by tenants	10,268	13,968	15,314
Initial measurement of operating right of use ground lease assets (Notes 2, 3 and 18)	96,348			96,272
Initial measurement of operating ground lease liabilities (Notes 2, 3 and 18)	98,400			$ 98,349
NON-CASH FINANCING TRANSACTIONS:
Accrual of dividends and distributions payable to common stockholders and common unitholders (Notes 14 and 28)	$ 53,219	$ 47,559	$ 43,448