Supplemental Cash Flow Information of the Operating Partnership (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $46,761 and $31,880 as of September 30, 2018 and 2017, respectively	$ 32,175	$ 46,878
Interest capitalized	46,761	31,880
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development properties	142,133	104,409
Assumption of accrued liabilities in connection with acquisitions (Note 2)	40,624	0
Tenant improvements funded directly by tenants	7,211	10,361
NON-CASH FINANCING TRANSACTIONS:
Accrual of distributions payable to common unitholders	47,411	43,324
Kilroy Realty L.P. [Member]
SUPPLEMENTAL CASH FLOWS INFORMATION:
Cash paid for interest, net of capitalized interest of $46,761 and $31,880 as of September 30, 2018 and 2017, respectively	32,175	46,878
Interest capitalized	46,761	31,880
NON-CASH INVESTING TRANSACTIONS:
Accrual for expenditures for operating properties and development properties	142,133	104,409
Assumption of accrued liabilities in connection with acquisitions (Note 2)	40,624	0
Tenant improvements funded directly by tenants	7,211	10,361
NON-CASH FINANCING TRANSACTIONS:
Accrual of distributions payable to common unitholders	$ 47,411	$ 43,324