Supplemental Cash Flow Information of the Operating Partnership - Reconciliation of cash and cash equivalents and restricted cash (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Other Significant Noncash Transactions [Line Items]
Cash and cash equivalents	$ 49,693	$ 51,604	$ 53,069	$ 57,649
Restricted cash	6,300	119,430	0	9,149
Cash and cash equivalents and restricted cash	55,993	171,034	53,069	66,798
Kilroy Realty L.P. [Member]
Other Significant Noncash Transactions [Line Items]
Cash and cash equivalents	49,693	51,604	53,069	57,649
Restricted cash	6,300	119,430	0	9,149
Cash and cash equivalents and restricted cash	$ 55,993	$ 171,034	$ 53,069	$ 66,798