Stockholders' Equity of the Company (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Dividends Payable [Line Items]
Aggregate gross proceeds		$ 31,117	$ 387,398	$ 102,229
Aggregate net proceeds after selling commissions	$ 249,600
Accrued dividend and distributions
Accrued dividends and distributions		222,306	34,992
Accrual of dividends and distributions payable to common stockholders and common unitholders		$ 220,650	$ 33,336	$ 31,243
Summary of shares and units
Common stock		93,219,439	92,258,690
Noncontrolling common units		2,381,543	1,764,775
Common stockholders and noncontrolling unitholders [Member]
Accrued dividend and distributions
Accrued dividends and distributions			$ 33,336
Common stock [Member]
Accrued dividend and distributions
Accrued dividends and distributions		$ 212,074	$ 32,291
Summary of shares and units
Common stock		93,219,439	92,258,690
Capital units [Member]
Accrued dividend and distributions
Accrued dividends and distributions		$ 5,418	$ 618
Preferred Stock [Member]
Accrued dividend and distributions
Accrued dividends and distributions		1,656	$ 1,656
Series G Preferred Stock [Member]
Summary of shares and units
Preferred units, issued			4,000,000
Preferred stock (in shares)			4,000,000
Series H Preferred Stock [Member]
Summary of shares and units
Preferred units, issued			4,000,000
Preferred stock (in shares)			4,000,000
Restricted Stock Units (RSUs) [Member]
Accrued dividend and distributions
Accrued dividends and distributions		$ 3,158	$ 427
Time-Based Restricted Stock Units (RSUs) [Member]
Summary of shares and units
RSUs		1,395,189	1,269,809
Issuance of Equity under ATM Program [Member] | Common stock [Member]
Dividends Payable [Line Items]
Share of common stock sold during the period		451,398	1,866,267	1,599,123
Aggregate gross proceeds		$ 32,300	$ 140,100	$ 104,700
Aggregate net proceeds after selling commissions		31,900	138,200	103,100
Kilroy Realty, L.P. [Member]
Accrued dividend and distributions
Accrued dividends and distributions		$ 222,306	$ 34,992
Accrual of dividends and distributions payable to common stockholders and common unitholders				$ 31,243
Kilroy Realty, L.P. [Member] | Capital units [Member]
Summary of shares and units
Noncontrolling common units		2,381,543	1,764,775
Kilroy Realty, L.P. [Member] | Restricted Stock Units (RSUs) [Member]
Accrued dividend and distributions
Accrued dividends and distributions			$ 427
Kilroy Realty, L.P. [Member] | Market measure-based Restricted Stock Units (RSUs) [Member]
Summary of shares and units
Number of RSUs outstanding		659,051	425,452