Secured and Unsecured Debt of the Operating Partnership Secured and Unsecured Debt of the Operating Partnership - Secured Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	$ 546,292,000		$ 560,434,000
Debt premium	10,300,000
Secured Debt [Member]
Secured Debt
Debt premium	10,300,000		14,600,000
Secured Debt [Member] | 4.27% Mortgage Payable due Feb 1, 2018 [Member]
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	130,800,000
Secured Debt [Member] | 4.48% Mortgage Payable due July 2027
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	97,000,000
Secured Debt [Member] | 6.05% Mortgage Payable Due June 1, 2019 [Member]
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	81,200,000
Secured Debt [Member] | 6.51% Mortgage Payable due February 1, 2017 [Member]
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	66,600,000
Secured Debt [Member] | 5.23% Mortgage Payable due January 2016 [Member]
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	51,900,000
Secured Debt [Member] | 5.57% Mortgage Note Payable due February 2016 [Member]
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	39,300,000
Secured Debt [Member] | 5.09% Mortgage Payable due August 2015 [Member] [Member]
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	34,000,000
Secured Debt [Member] | 4.94% Mortgage Payable due April 15, 2015 [Member]
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	26,200,000
Secured Debt [Member] | 7.15% Mortgage Payable due May 1, 2017 [Member]
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	6,600,000
Kilroy Realty, L.P. [Member]
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	546,292,000		560,434,000
Kilroy Realty, L.P. [Member] | Secured Debt [Member]
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	546,292,000	[1]	560,434,000	[1]
Debt premium			11,600,000
Number of properties used as collateral for secured debbt	31		21
Net book value of properties pledged as collateral for secured debt	1,600,000,000		1,000,000,000
Number of secured loans with restrictions	9
Number of secured debt	10
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 4.27% Mortgage Payable due Feb 1, 2018 [Member]
Secured Debt
Stated interest rate	4.27%	[2]
Effective interest rate	4.27%	[2],[3]
Maturity date	Feb. 01, 2018
Secured debt (Notes 3, 6, 7 and 16)	130,767,000		133,117,000
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 4.48% Mortgage Payable due July 2027
Secured Debt
Stated interest rate	4.48%	[2]
Effective interest rate	4.48%	[2],[3]
Maturity date	Jul. 01, 2027
Secured debt (Notes 3, 6, 7 and 16)	97,000,000	[4]	97,000,000	[4]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 6.05% Mortgage Payable Due June 1, 2019 [Member]
Secured Debt
Stated interest rate	6.05%	[2]
Effective interest rate	3.50%	[2],[3]
Maturity date	Jun. 01, 2019
Secured debt (Notes 3, 6, 7 and 16)	89,242,000	[1]	92,502,000	[1]
Debt premium	8,000,000		9,900,000
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 6.51% Mortgage Payable due February 1, 2017 [Member]
Secured Debt
Stated interest rate	6.51%	[2]
Effective interest rate	6.51%	[2],[3]
Maturity date	Feb. 01, 2017
Secured debt (Notes 3, 6, 7 and 16)	66,647,000	[1]	67,663,000	[1]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 5.23% Mortgage Payable due January 2016 [Member]
Secured Debt
Stated interest rate	5.23%	[2]
Effective interest rate	3.50%	[2],[3]
Maturity date	Jan. 01, 2016
Secured debt (Notes 3, 6, 7 and 16)	52,793,000	[1]	54,570,000	[1]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 5.57% Mortgage Note Payable due February 2016 [Member]
Secured Debt
Stated interest rate	5.57%	[2]
Effective interest rate	3.25%	[2],[3]
Maturity date	Feb. 11, 2016
Secured debt (Notes 3, 6, 7 and 16)	40,258,000	[1]	41,654,000	[1]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 5.09% Mortgage Payable due August 2015 [Member] [Member]
Secured Debt
Stated interest rate	5.09%	[2]
Effective interest rate	3.50%	[2],[3]
Maturity date	Aug. 07, 2015
Secured debt (Notes 3, 6, 7 and 16)	34,311,000	[1]	34,845,000	[1]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 4.94% Mortgage Payable due April 15, 2015 [Member]
Secured Debt
Stated interest rate	4.94%	[2]
Effective interest rate	4.00%	[2],[3]
Maturity date	Apr. 15, 2015
Secured debt (Notes 3, 6, 7 and 16)	26,285,000	[1]	27,641,000	[1]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 7.15% Mortgage Payable due May 1, 2017 [Member]
Secured Debt
Stated interest rate	7.15%	[2]
Effective interest rate	7.15%	[2],[3]
Maturity date	May 01, 2017
Secured debt (Notes 3, 6, 7 and 16)	6,568,000	[1]	8,972,000	[1]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | Other [Member]
Secured Debt
Secured debt (Notes 3, 6, 7 and 16)	$ 2,421,000	[1]	$ 2,470,000	[1]

[1] Amounts reported include the amounts of unamortized debt premiums of $10.3 million and $14.6 million as of December 31, 2014 and 2013, 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] In January 2013, in connection with the acquisition of two office buildings in Seattle, Washington, we assumed a mortgage loan that is secured by the project. The loan requires monthly principal and interest payments based on a 6.4 year amortization period. As of December 31, 2014 and 2013, the mortgage loan had unamortized debt premiums of $8.0 million and $9.9 million, respectively.