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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Capitalized Interest and Loan Fees [Line Items]
Interest Expense	$ 12,819	$ 16,608	$ 44,561	$ 49,880
Kilroy Realty, L.P. [Member]
Capitalized Interest and Loan Fees [Line Items]
Gross interest expense	27,386	29,936	82,322	85,740
Capitalized interest	(14,567)	(13,328)	(37,761)	(35,860)
Interest Expense	$ 12,819	$ 16,608	$ 44,561	$ 49,880