Unsecured Revolving Credit Facility (Details 3) (USD $)					3 Months Ended		9 Months Ended				12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Kilroy Realty, L.P. [Member]	Dec. 31, 2012 Kilroy Realty, L.P. [Member]	Sep. 30, 2013 Kilroy Realty, L.P. [Member] Revolving Credit Facility [Member]		Sep. 30, 2013 Kilroy Realty, L.P. [Member] Revolving Credit Facility [Member]		Dec. 31, 2012 Kilroy Realty, L.P. [Member] Revolving Credit Facility [Member]		Dec. 31, 2012 Kilroy Realty, L.P. [Member] Line of Credit [Member]
Line of Credit Facility [Line Items]
Unsecured debt additional borrowing amount					$ 200,000,000
Terms of the Credit Facility
Unsecured line of credit	0	185,000,000	0	185,000,000	0		0		185,000,000
Remaining borrowing capacity					500,000,000		500,000,000		315,000,000
Total borrowing capacity					500,000,000	[1]	500,000,000	[1]	500,000,000	[1]
Interest rate									1.66%	[2]
Facility fee - annual rate					0.30%	[3]
Maturity date					Apr. 03, 2017	[4]
Debt Instrument, Basis Spread on Variable Rate							1.45%
Debt Issuance Cost											$ 10,200,000

[1] We may elect to borrow, subject to bank approval, up to an additional $200.0 million under an accordion feature under the terms of the revolving credit facility.

[2] The revolving credit facility interest rate was calculated based on an annual rate of LIBOR plus 1.450% as of both September 30, 2013 and December 31, 2012. No interest rate is shown as of September 30, 2013 because no borrowings were outstanding.

[3] The facility fee is paid on a quarterly basis and is calculated based on the total borrowing capacity. In addition to the facility fee, from 2010 to 2012 we incurred debt origination and legal costs totaling approximately $10.2 million that are currently being amortized through the maturity date of the revolving credit facility.

[4] Under the terms of the revolving credit facility, we may exercise an option to extend the maturity date by one year.