Secured and Unsecured Debt of the Operating Partnership - Capitalized Interest and Loan Fees (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Capitalized Interest and Loan Fees [Line Items]
Interest expense	$ 11,727	$ 12,712	$ 22,970	$ 26,210
Kilroy Realty L.P. [Member]
Capitalized Interest and Loan Fees [Line Items]
Gross interest expense	32,607	28,523	63,287	55,603
Capitalized interest and deferred financing costs	(20,880)	(15,811)	(40,317)	(29,393)
Interest expense	$ 11,727	$ 12,712	$ 22,970	$ 26,210