Secured and Unsecured Debt of the Operating Partnership (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013		Sep. 30, 2013		Dec. 31, 2012
Debt Instrument [Line Items]
Secured Debt	$ 563,898,000	[1]	$ 563,898,000	[1]	$ 561,096,000	[1]
Kilroy Realty, L.P. [Member]
Debt Instrument [Line Items]
Secured Debt	563,898,000		563,898,000		561,096,000
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	4.27%	[2]	4.27%	[2]
GAAP Effective Rate	4.27%	[2],[3]	4.27%	[2],[3]
Maturity Date			Feb. 01, 2018
Secured Debt	133,689,000	[1]	133,689,000	[1]	135,000,000	[1]
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	4.48%	[2]	4.48%	[2]
GAAP Effective Rate	4.48%	[2],[3]	4.48%	[2],[3]
Maturity Date			Jul. 01, 2027
Secured Debt	97,000,000	[1],[4]	97,000,000	[1],[4]	97,000,000	[1],[4]
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	6.05%	[2]	6.05%	[2]
GAAP Effective Rate	3.50%	[2],[3]	3.50%	[2],[3]
Maturity Date			Jun. 01, 2019
Secured Debt	93,306,000	[1],[4],[5]	93,306,000	[1],[4],[5]	0	[1],[4],[5]
Principal amount of secured debt	83,900,000		83,900,000
Debt premium	11,600,000		11,600,000
Amortization period of debt	6 years 5 months
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 6.37% Mortgage Payable due April 01, 2013 [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	6.37%	[2]	6.37%	[2]
GAAP Effective Rate	3.55%	[2],[3]	3.55%	[2],[3]
Maturity Date			Apr. 01, 2013
Secured Debt	0	[1],[6]	0	[1],[6]	83,116,000	[1],[6]
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	6.51%	[2]	6.51%	[2]
GAAP Effective Rate	6.51%	[2],[3]	6.51%	[2],[3]
Maturity Date			Feb. 01, 2017
Secured Debt	67,907,000	[1]	67,907,000	[1]	68,615,000	[1]
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	5.23%	[2]	5.23%	[2]
GAAP Effective Rate	3.50%	[2],[3]	3.50%	[2],[3]
Maturity Date			Jan. 01, 2016
Secured Debt	55,007,000	[1],[4]	55,007,000	[1],[4]	56,302,000	[1],[4]
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	5.57%	[2]	5.57%	[2]
GAAP Effective Rate	3.25%	[2],[3]	3.25%	[2],[3]
Maturity Date			Feb. 11, 2016
Secured Debt	41,999,000	[1],[4]	41,999,000	[1],[4]	43,016,000	[1],[4]
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	5.09%	[2]	5.09%	[2]
GAAP Effective Rate	3.50%	[2],[3]	3.50%	[2],[3]
Maturity Date			Aug. 07, 2015
Secured Debt	34,979,000	[1],[4]	34,979,000	[1],[4]	35,379,000	[1],[4]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 4.94% Mortgage Payable due April 15, 2015 [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	4.94%	[2]	4.94%	[2]
GAAP Effective Rate	4.00%	[2],[3]	4.00%	[2],[3]
Maturity Date			Apr. 15, 2015
Secured Debt	27,970,000	[1],[4]	27,970,000	[1],[4]	28,941,000	[1],[4]
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	7.15%	[2]	7.15%	[2]
GAAP Effective Rate	7.15%	[2],[3]	7.15%	[2],[3]
Maturity Date			May 01, 2017
Secured Debt	9,546,000	[1]	9,546,000	[1]	11,210,000	[1]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | Municipal Bonds [Member]
Debt Instrument [Line Items]
Secured Debt	$ 2,495,000	[1]	$ 2,495,000	[1]	$ 2,517,000	[1]

[1] Amounts reported include the amounts of unamortized debt premiums and discounts for the periods presented.

[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] 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 assumed mortgage had a principal balance of $83.9 million at the acquisition date and was recorded at fair value on the date of the acquisition resulting in a premium of approximately $11.6 million. The loan requires monthly principal and interest payments based on a 6.4 year amortization period.

[6] In January 2013, we repaid this loan prior to the stated maturity date.