Secured and Unsecured Debt of the Operating Partnership - Capitalized Interest and Loan Fees (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Capitalized Interest and Loan Fees [Line Items]
Interest expense	$ 11,075	$ 16,151	$ 37,285	$ 51,476
Kilroy Realty L.P. [Member]
Capitalized Interest and Loan Fees [Line Items]
Gross interest expense	30,231	28,331	85,834	84,577
Capitalized interest and deferred financing costs	(19,156)	(12,180)	(48,549)	(33,101)
Interest expense	$ 11,075	$ 16,151	$ 37,285	$ 51,476