Secured and Unsecured Debt of the Operating Partnership Capitalized Interest and Loan Fees (Details 5) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Capitalized Interest and Loan Fees [Line Items]
Interest Expense	$ 18,853	$ 19,854	$ 58,021	$ 60,172
Kilroy Realty, L.P. [Member]
Capitalized Interest and Loan Fees [Line Items]
Gross interest expense	27,942	24,843	83,322	73,326
Capitalized interest	(9,089)	(4,989)	(25,301)	(13,154)
Interest Expense	$ 18,853	$ 19,854	$ 58,021	$ 60,172