Secured and Unsecured Debt of the Operating Partnership - Unsecured Revolving Credit Facility (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Unsecured Debt		$ 1,856,590	$ 1,783,121
Terms of the Credit Facility
Outstanding borrowings		0	140,000
Kilroy Realty, L.P. [Member]
Line of Credit Facility [Line Items]
Unsecured Debt		1,856,590	1,783,121
Terms of the Credit Facility
Outstanding borrowings		0	140,000
Revolving Credit Facility [Member] | Kilroy Realty, L.P. [Member]
Terms of the Credit Facility
Outstanding borrowings		0	140,000
Remaining borrowing capacity		600,000	460,000
Total borrowing capacity		$ 600,000	$ 600,000
Interest rate		0.00%	1.41%
Facility fee - annual rate		0.20%	0.25%
Maturity date		Jul. 01, 2019
Unsecured debt additional borrowing amount		$ 311,000
Spread on variable rate		1.05%	1.25%
Debt Issuance Cost		$ 4,600
$150.0 Term Loan Facility [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Unsecured Debt		150,000
$150.0 Term Loan Facility [Member] | Line of Credit [Member] | Kilroy Realty, L.P. [Member]
Line of Credit Facility [Line Items]
Unsecured Debt		$ 150,000	$ 150,000
Terms of the Credit Facility
Spread on variable rate	[1]	1.40%	1.56%
Debt Instrument, Maturity Date		Jul. 01, 2019	Jul. 01, 2019
London Interbank Offered Rate (LIBOR) [Member] | $150.0 Term Loan Facility [Member] | Line of Credit [Member] | Kilroy Realty, L.P. [Member]
Terms of the Credit Facility
Spread on variable rate		1.15%	1.40%

[1] Our unsecured term loan facility interest rate was calculated based on an annual rate of LIBOR plus 1.150% and LIBOR plus 1.400% as of December 31, 2015 and December 31, 2014, respectively.