Secured Debt (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Secured Debt	[1]	$ 475,923	$ 546,292
Secured Debt [Member]
Debt Instrument [Line Items]
Unamortized premium		7,200	10,300
Kilroy Realty, L.P. [Member]
Debt Instrument [Line Items]
Secured Debt		$ 475,923	546,292
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 4.27% Mortgage Payable due Feb. 01, 2018 [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	[2]	4.27%
Effective interest rate	[2],[3]	4.27%
Maturity Date		Feb. 01, 2018
Secured Debt	[1]	$ 128,937	130,767
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 4.48% Mortgage Payable due July 1, 2027 [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	[2],[4]	4.48%
Effective interest rate	[2],[3],[4]	4.48%
Maturity Date		Jul. 01, 2027
Secured Debt	[1],[4]	$ 96,743	97,000
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 6.05% Mortgage Payable Due June 1, 2019 [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	[2]	6.05%
Effective interest rate	[2],[3],[4]	3.50%
Maturity Date		Jun. 01, 2019
Secured Debt	[1],[4]	$ 86,737	89,242
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 6.51% Mortgage Payable due Feb. 01, 2017 [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	[2]	6.51%
Effective interest rate	[2],[3]	6.51%
Maturity Date		Feb. 01, 2017
Secured Debt	[1]	$ 65,841	66,647
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 5.23% Mortgage Payable due Jan. 01, 2016 [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	[2],[4],[5]	5.23%
Effective interest rate	[2],[3],[4],[5]	3.50%
Maturity Date		Jan. 01, 2016
Secured Debt	[1],[4]	$ 51,431	52,793
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 5.57% Morgage Payable Due Feb. 11, 2016 [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	[2],[4],[5]	5.57%
Effective interest rate	[2],[3],[4],[5]	3.25%
Maturity Date		Feb. 11, 2016
Secured Debt	[1],[4]	$ 39,188	40,258
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 5.09% Mortgage Payable due Aug. 7, 2015 [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	[2],[6]	5.09%
Effective interest rate	[2],[3],[6]	3.50%
Maturity Date		Aug. 07, 2015
Secured Debt	[1],[5]	$ 0	34,311
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | Four Point Nine four Percent Mortgage Payable due April Fifteen Two Thousand Fifteen [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	[2],[6]	4.94%
Effective interest rate	[2],[3],[6]	4.00%
Maturity Date		Apr. 15, 2015
Secured Debt	[1],[5]	$ 0	26,285
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 7.15% Mortgage Payable due May 01, 2017 [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	[2]	7.15%
Effective interest rate	[2],[3]	7.15%
Maturity Date		May 01, 2017
Secured Debt	[1]	$ 4,649	6,568
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | Municipal Bonds [Member]
Debt Instrument [Line Items]
Secured Debt	[1]	$ 2,397	$ 2,421

[1] Amounts reported include the amounts of unamortized debt premiums of $7.2 million and $10.3 million as of September 30, 2015 and December 31, 2014, respectively.

[2] All interest rates presented are fixed-rate interest rates.

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

[4] The secured debt and the related properties that secure the debt are held in a special purpose entity and the properties are not available to satisfy the debts and other obligations of the Company or the Operating Partnership.

[5] These mortgage notes payable were repaid in October 2015 at par.

[6] These mortgage notes payable were repaid during the nine months ended September 30, 2015 at par.