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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Capitalized Interest and Loan Fees [Line Items]
Interest expense	$ 16,105	$ 19,468	$ 59,829	$ 49,796
Kilroy Realty L.P. [Member]
Capitalized Interest and Loan Fees [Line Items]
Gross interest expense	39,552	38,807	118,257	111,069
Capitalized interest and deferred financing costs	(23,447)	(19,339)	(58,428)	(61,273)
Interest expense	$ 16,105	$ 19,468	$ 59,829	$ 49,796