Supplemental Cash Flow Information of the Operating Partnership - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Roll Forward]
Cash and cash equivalents	$ 731,991	$ 60,044	$ 51,604	$ 57,649
Restricted cash	91,139	16,300	119,430	9,149
Cash and cash equivalents and restricted cash	823,130	76,344	171,034	66,798
Kilroy Realty L.P. [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Roll Forward]
Cash and cash equivalents	731,991	60,044	51,604	57,649
Restricted cash	91,139	16,300	119,430	9,149
Cash and cash equivalents and restricted cash	$ 823,130	$ 76,344	$ 171,034	$ 66,798