Stockholders' Equity of the Company - At-The-Market Offering and Derivatives and Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Dividends Payable [Line Items]
Aggregate net proceeds after selling commissions	$ 353,722	$ 130,693	$ 326,058
Accrued dividend and distributions
Accrued dividends and distributions	$ 53,219	$ 47,559
Summary of shares and units
Common stock	106,016,287	100,746,988
Restricted Stock Units (RSUs) [Member]
Summary of shares and units
RSUs	1,651,905	1,711,628
Common stockholders and noncontrolling unitholders [Member]
Accrued dividend and distributions
Accrued dividends and distributions	$ 53,219	$ 47,559
Common Stock [Member]
Accrued dividend and distributions
Accrued dividends and distributions	$ 51,418	$ 45,840
Summary of shares and units
Common stock	106,016,287	100,746,988
Common units [Member]
Accrued dividend and distributions
Accrued dividends and distributions	$ 981	$ 922
Issuance of Equity under ATM Program [Member]
Dividends Payable [Line Items]
Shares of common stock sold during the period (in shares)		1,817,195	235,077
Weighted average price per share of common stock (in dollars per share)		$ 73.64	$ 75.40
Aggregate gross proceeds		$ 133,800	$ 17,700
Aggregate net proceeds after selling commissions		132,100	17,500
Kilroy Realty L.P. [Member]
Dividends Payable [Line Items]
Aggregate net proceeds after selling commissions	353,722	130,693	$ 326,058
Accrued dividend and distributions
Accrued dividends and distributions	53,219	47,559
Kilroy Realty L.P. [Member] | Restricted Stock Units (RSUs) [Member]
Accrued dividend and distributions
Accrued dividends and distributions	$ 820	$ 797
Kilroy Realty L.P. [Member] | Market measure-based Restricted Stock Units (RSUs) [Member]
Summary of shares and units
Number of RSUs outstanding (in shares)	932,675	1,018,337
Kilroy Realty L.P. [Member] | Common units [Member]
Summary of shares and units
Noncontrolling common units (in units)	2,023,287	2,025,287