Secured and Unsecured Debt of the Operating Partnership - Exchangeable Senior Notes (Details Textuals)	3 Months Ended			12 Months Ended
	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 $ / option shares	Dec. 31, 2013 USD ($) shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) $ / shares $ / option shares		Dec. 31, 2013 USD ($) $ / shares	Jun. 30, 2015 USD ($)	Nov. 13, 2014 USD ($)
Debt Instrument [Line Items]
Average Trading Price Of The Companys Stock | $ / shares					$ 60.04	[1]	$ 52.12
Derivative, Price Risk Option Strike Price | $ / option		42.81			42.81
Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Debt Instrument, Periodic Payment, Interest					$ 5,608,000		$ 7,331,000
Amortization of Debt Discount (Premium)					3,769,000		4,427,000
Interest Expense, Debt					$ 9,377,000		11,758,000
Kilroy Realty, L.P. [Member] | Exchangeable Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross									$ 135,500,000
Kilroy Realty, L.P. [Member] | Exchangeable Notes [Member] | Exchangeable Note Two [Member]
Debt Instrument [Line Items]
Exchangeable note repurchased prinicipal amount			$ 0				$ 0	$ 0
Kilroy Realty, L.P. [Member] | Exchangeable Notes [Member] | Notes exchanged during 2014 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 37,000,000			$ 37,000,000
Common Stock
Debt Instrument [Line Items]
Stock Issued During Period, Shares, Conversion of Convertible Securities | shares	1,660,053	431,270
Shares of Common stock exercised in the capped call option | shares			404,136		111,206
Stock issued during period, shares, conversion of convertible securities, net of adjustments | shares				1,255,917
Common Stock, Issued, Net of Capped Calls | shares		320,064		1,575,981

[1] Period Ended November 15, 2014(1) Year Ended December 31, 2013Per share average trading price of the Company's common stock$60.04 $52.12_______________(1) Represents the maturity date of the 4.25% Exchangeable Notes.