Supplemental Cash Flow Information of the Operating Partnership - Supplemental Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $18,901 and $13,051 as of March 31, 2019 and 2018, respectively	$ 4,706	$ 9,699
Capitalized interest	18,901	13,051
Cash paid for amounts included in the measurement of ground lease liabilities	1,220	1,239
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development properties	87,038	57,155
Tenant improvements funded directly by tenants	2,682	2,014
Operating right of use ground lease asset	82,794		$ 82,938
Operating ground lease liabilities	87,247		87,409
NON-CASH FINANCING TRANSACTIONS:
Accrual of distributions payable to common unitholders	47,676	43,512
Kilroy Realty L.P. [Member]
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $18,901 and $13,051 as of March 31, 2019 and 2018, respectively	4,706	9,699
Capitalized interest	18,901	13,051
Cash paid for amounts included in the measurement of ground lease liabilities	1,220	1,239
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development properties	87,038	57,155
Tenant improvements funded directly by tenants	2,682	2,014
Operating right of use ground lease asset	82,794		82,938
Operating ground lease liabilities	87,247		$ 87,409
NON-CASH FINANCING TRANSACTIONS:
Accrual of distributions payable to common unitholders	$ 47,676	$ 43,512