Preferred and Common Units of the Operating Partnership (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Aggregate gross proceeds		$ 31,117	$ 387,398	$ 102,229
Aggregate net proceeds after selling commissions	$ 249,600
Summary of units
Company owned general partnership interest		97.50%	98.10%
Noncontrolling common units of the Operating Partnership		2,381,543	1,764,775
Ownership interest of noncontrolling interest		2.50%	1.90%
Accrued distributions
Accrued dividends and distributions		$ 222,306	$ 34,992
Restricted Stock Units (RSUs) [Member]
Accrued distributions
Accrued dividends and distributions		3,158	427
Common stock [Member]
Accrued distributions
Accrued dividends and distributions		212,074	32,291
Capital units [Member]
Accrued distributions
Accrued dividends and distributions		5,418	618
Kilroy Realty, L.P. [Member]
Accrued distributions
Accrued dividends and distributions		$ 222,306	$ 34,992
Kilroy Realty, L.P. [Member] | Restricted Stock Units (RSUs) [Member]
Summary of units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number		1,395,189	1,269,809
Accrued distributions
Accrued dividends and distributions			$ 427
Kilroy Realty, L.P. [Member] | Market measure-based Restricted Stock Units (RSUs) [Member]
Summary of units
Number of RSUs outstanding		659,051	425,452
Kilroy Realty, L.P. [Member] | Partners Capital Common Unit [Member]
Class of Stock [Line Items]
Common units exchanged for share of common stock by the Company				1,950,599
Accrued distributions
Accrued dividends and distributions		$ 220,650	$ 33,336
Kilroy Realty, L.P. [Member] | Partners capital general partner [Member]
Accrued distributions
Accrued dividends and distributions		212,074	32,291
Kilroy Realty, L.P. [Member] | Partners capital limited partner [Member]
Accrued distributions
Accrued dividends and distributions		5,418	618
Kilroy Realty, L.P. [Member] | Partners Capital Preferred Units [Member]
Accrued distributions
Accrued dividends and distributions		$ 1,656	$ 1,656
Kilroy Realty, L.P. [Member] | Series G Cumulative Redeemable Preferred Unit [Member]
Summary of units
Preferred units outstanding		4,000,000	4,000,000
Kilroy Realty, L.P. [Member] | Series H Cumulative Redeemable Preferred Unit [Member]
Summary of units
Preferred units outstanding		4,000,000	4,000,000
Kilroy Realty, L.P. [Member] | Capital units [Member]
Summary of units
Company owned common units in the Operating Partnership		93,219,439	92,258,690
Noncontrolling common units of the Operating Partnership		2,381,543	1,764,775
Issuance of Equity under ATM Program [Member] | Partners Capital Common Unit [Member]
Class of Stock [Line Items]
Common units exchanged for share of common stock by the Company		451,398	1,866,267	1,599,123
Issuance of Equity under ATM Program [Member] | Common stock [Member]
Class of Stock [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