Secured and Unsecured Debt of the Operating Partnership (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Debt Instrument [Line Items]
Secured Debt	$ 570,676,000	[1]	$ 561,096,000	[1]
Kilroy Realty, L.P. [Member]
Debt Instrument [Line Items]
Secured Debt	570,676,000		561,096,000
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | Four Point Two Seven Percent Mortgage Payable due Feb One Two Thousand Eighteen 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		Feb. 01, 2018
Secured Debt	134,815,000	[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]	4.48%	[2],[4]
GAAP Effective Rate	4.48%	[2],[3],[4]	4.48%	[2],[3],[4]
Maturity Date	Jul. 01, 2027	[4]	Jul. 01, 2027	[4]
Secured Debt	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],[4],[5]		[2],[4],[5]
GAAP Effective Rate	3.50%	[2],[3],[4],[5]		[2],[3],[4],[5]
Maturity Date	Jun. 01, 2019	[4],[5]
Secured Debt	94,896,000	[1],[4],[5]	0	[1],[4],[5]
Principal amount of secured debt	83,900,000
Debt premium	11,600,000
Amortization period of debt	6 years 5 months
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | Six Point Thirty Seven Percent Mortgage Payable due April First Two Thousand Thirteen [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	6.37%	[2],[6]	6.37%	[2],[6]
GAAP Effective Rate	3.55%	[2],[3],[6]	3.55%	[2],[3],[6]
Maturity Date	Apr. 01, 2013	[6]	Apr. 01, 2013	[6]
Secured Debt	0	[1],[6]	83,116,000	[1],[6]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | Six Point Five One Percent Mortgage Payable due February One Two Thousand Seventeen [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		Feb. 01, 2017
Secured Debt	68,383,000	[1]	68,615,000	[1]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | Five Point Twenty Three Percent Mortgage Payable due January First Two Thousand Sixteen [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	5.23%	[2],[4]	5.23%	[2],[4]
GAAP Effective Rate	3.50%	[2],[3],[4]	3.50%	[2],[3],[4]
Maturity Date	Jan. 01, 2016	[4]	Jan. 01, 2016	[4]
Secured Debt	55,863,000	[1],[4]	56,302,000	[1],[4]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | Five Point Five Seven Percent Morgage Payable Due February Two Thousand Sixteen [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	5.57%	[2],[4]	5.57%	[2],[4]
GAAP Effective Rate	3.25%	[2],[3],[4]	3.25%	[2],[3],[4]
Maturity Date	Feb. 11, 2016	[4]	Feb. 11, 2016	[4]
Secured Debt	42,672,000	[1],[4]	43,016,000	[1],[4]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | 5.09% Mortgage Payable due August 7, 2015 [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	5.09%	[2],[4]	5.09%	[2],[4]
GAAP Effective Rate	3.50%	[2],[3],[4]	3.50%	[2],[3],[4]
Maturity Date	Aug. 07, 2015	[4]	Aug. 07, 2015	[4]
Secured Debt	35,245,000	[1],[4]	35,379,000	[1],[4]
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	4.94%	[2],[4]	4.94%	[2],[4]
GAAP Effective Rate	4.00%	[2],[3],[4]	4.00%	[2],[3],[4]
Maturity Date	Apr. 15, 2015	[4]	Apr. 15, 2015	[4]
Secured Debt	28,620,000	[1],[4]	28,941,000	[1],[4]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | Seven Point Fifteen Percent Mortgage Payable due May One Two Thousand Seventeen [Member]
Debt Instrument [Line Items]
Annual Stated Interest Rate	7.15%	[2]	7.15%
GAAP Effective Rate	7.15%	[2],[3]	7.15%	[2],[3]
Maturity Date	May 01, 2017		May 01, 2017
Secured Debt	10,665,000	[1]	11,210,000	[1]
Kilroy Realty, L.P. [Member] | Secured Debt [Member] | Municipal Bonds [Member]
Debt Instrument [Line Items]
Secured Debt	$ 2,517,000	[1],[7]	$ 2,517,000	[1],[7]
Interest rates range, minimum	4.74%
Interest rates range, maximum	6.19%

[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.

[7] The public facility bonds (the “Bonds”), the proceeds from which were used to finance infrastructure improvements on one of the Company’s undeveloped land parcels, were issued in February 2008 by the City of Carlsbad. The Bonds have annual maturities from September 1, 2013 through September 1, 2038, with interest rates ranging from 4.74% to 6.19%. Principal and interest payments for the Bonds will be charged through the assessment of special property taxes.