Supplemental Cash Flow Information of the Operating Partnership - Reconciliation of cash and cash equivalents and restricted cash (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Other Significant Noncash Transactions [Line Items]
Cash and cash equivalents	$ 86,517	$ 57,649	$ 64,954	$ 193,418
Restricted cash	0	9,149	179,276	56,711
Cash and cash equivalents and restricted cash	86,517	66,798	244,230	250,129
Kilroy Realty L.P. [Member]
Other Significant Noncash Transactions [Line Items]
Cash and cash equivalents	86,517	57,649	64,954	193,418
Restricted cash	0	9,149	179,276	56,711
Cash and cash equivalents and restricted cash	$ 86,517	$ 66,798	$ 244,230	$ 250,129