Unsecured Senior Notes (Details) (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Debt Instrument [Line Items]
Unsecured debt	$ 1,783,280,000				$ 1,783,121,000
Kilroy Realty, L.P. [Member]
Debt Instrument [Line Items]
Unsecured debt	1,783,280,000				1,783,121,000
Kilroy Realty, L.P. [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.25%
Debt Instrument, Contingent Additional Borrowings	311,000,000
Kilroy Realty, L.P. [Member] | Four Point Two Five Zero Percent Unsecured Senior Notes [Member] [Domain] | Senior Notes [Member]
Debt Instrument [Line Items]
Stated coupon rate	4.25%
Effective interest rate	4.35%	[1],[2]
Debt Instrument, Face Amount	400,000,000				400,000,000
Debt Instrument, Unamortized Discount	(4,273,000)				(4,348,000)
Unsecured debt	395,727,000				395,652,000
Kilroy Realty, L.P. [Member] | 3.800% Unsecured Senior Note [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Stated coupon rate	3.80%
Effective interest rate	3.804%	[1],[3]
Debt Instrument, Face Amount	300,000,000				300,000,000
Debt Instrument, Unamortized Discount	(77,000)				(79,000)
Unsecured debt	299,923,000				299,921,000
Kilroy Realty, L.P. [Member] | 4.800% Unsecured Senior Notes Due July Fifteen Two Thousand Eighteen [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Stated coupon rate	4.80%
Effective interest rate	4.827%	[1],[3]
Debt Instrument, Face Amount	325,000,000				325,000,000
Debt Instrument, Unamortized Discount	(246,000)				(265,000)
Unsecured debt	324,754,000				324,735,000
Kilroy Realty, L.P. [Member] | 6.625% Unsecured Senior Notes due June 1 2020 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Stated coupon rate	6.625%
Effective interest rate	6.743%	[1],[4]
Debt Instrument, Face Amount	250,000,000				250,000,000
Debt Instrument, Unamortized Discount	(1,101,000)				(1,154,000)
Unsecured debt	248,899,000				248,846,000
Kilroy Realty, L.P. [Member] | 5.000% Unsecured Senior Notes due Nov3 2015 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Stated coupon rate	5.00%
Effective interest rate	5.014%	[1],[5]
Debt Instrument, Face Amount	325,000,000				325,000,000
Debt Instrument, Unamortized Discount	(23,000)				(33,000)
Unsecured debt	324,977,000				324,967,000
Kilroy Realty, L.P. [Member] | Term Loan Facility [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Unsecured debt	$ 150,000,000				$ 150,000,000
Debt Instrument, Basis Spread on Variable Rate			1.56%	[6]

[1] This represents the rate at which interest expense is recorded for financial reporting purposes, which reflects the amortization of initial issuance discounts, excluding debt issuance costs.

[2] Interest on these notes is payable semi-annually in arrears on February 15th and August 15th of each year.

[3] Interest on these notes is payable semi-annually in arrears on January 15th and July 15th of each year.

[4] Interest on these notes is payable semi-annually in arrears on June 1st and December 1st of each year.

[5] Interest on these notes is payable semi-annually in arrears on May 3rd and November 3rd of each year.

[6] Our unsecured term loan facility interest rate was calculated based on an annual rate of LIBOR plus 1.40%.