Noncontrolling Interests on the Company's Consolidated Financial Statements - Common Units of the Operating Partnership (Details) $ / shares in Units, $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($) trading_day $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2017 shares
Noncontrolling Interest [Line Items]
Common limited partnership interest in the Operating Partnership	2.00%	2.10%	2.10%
Common stock, par value (in dollars per share) \| $ / shares	$ 0.01	$ 0.01
Number of trading days \| trading_day	10
Aggregate value upon redemption of outstanding noncontrolling common units \| $	$ 143.4	$ 154.5
Kilroy Realty L.P. [Member] \| Common units [Member]
Noncontrolling Interest [Line Items]
Common units outstanding held by common limited partners \| shares	2,025,287	2,077,193	2,077,193
Operating Partnership [Member]
Noncontrolling Interest [Line Items]
Common general partnership interest in the Operating Partnership	98.00%	97.90%	97.90%

Face amount or stated value per share of common stock.

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