Partners' Capital of the Operating Partnership (Details) - shares	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
General Partners' Capital Account [Abstract]
Ownership interest of noncontrolling interest	2.00%	2.10%	2.10%
Kilroy Realty L.P. [Member] | Common units [Member]
General Partners' Capital Account [Abstract]
Company owned common units in the Operating Partnership	100,746,988	98,620,333	98,382,256
Noncontrolling common units of the Operating Partnership	2,025,287	2,077,193	2,077,193
Operating Partnership [Member]
General Partners' Capital Account [Abstract]
Company owned general partnership interest	98.00%	97.90%	97.90%