Basis of Presentation and Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) building project	Dec. 31, 2014 USD ($) building property	Dec. 31, 2013 USD ($) building	Dec. 31, 2011
Basis of presentation and significant accounting policies [Line Items]
Proceeds from Sale of Real Estate Held-for-investment	$ 319,639,000	$ 427,544,000	$ 21,178,000
Number of Real Estate Properties Sold | building	10	17	3
Amortization of Financing Costs	$ 12,300,000	$ 12,200,000
Number of real estate properties	2	5
REIT annual taxable income distribution requirement percentage	90.00%			90.00%
Company annual taxable income distribution	100.00%
Concentration Risk of Significant Tenants, Percentage	36.90%
Cash, FDIC Insured Amount	$ 250,000
Kilroy Realty Finance, Inc. [Member]
Basis of presentation and significant accounting policies [Line Items]
Percentage of General partnership interest owned by wholly-owned subsidiary of the Company	1.00%
Torrey Santa Fe Properties [Member]
Basis of presentation and significant accounting policies [Line Items]
Number of real estate properties | project	4
Carlsbad Oaks [Member]
Basis of presentation and significant accounting policies [Line Items]
Number of real estate properties | project	1