Secured and Unsecured Debt of the Operating Partnership - Capitalized Interest and Loan Fees (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Capitalized Interest and Loan Fees [Line Items]
Interest expense	$ 11,243	$ 13,498
Kilroy Realty L.P. [Member]
Capitalized Interest and Loan Fees [Line Items]
Gross interest expense	30,680	27,080
Capitalized interest and deferred financing costs	(19,437)	(13,582)
Interest expense	$ 11,243	$ 13,498