Supplemental Cash Flow Information of the Operating Partnership - Reconciliation of Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH:
Cash and cash equivalents	$ 348,417	$ 731,991	$ 849,009	$ 60,044
Restricted cash	13,042	91,139	16,300	16,300
Cash and cash equivalents and restricted cash	361,459	823,130	865,309	76,344
Kilroy Realty L.P. [Member]
RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH:
Cash and cash equivalents	348,417	731,991	849,009	60,044
Restricted cash	13,042	91,139	16,300	16,300
Cash and cash equivalents and restricted cash	$ 361,459	$ 823,130	$ 865,309	$ 76,344