Partners' Capital of the Operating Partnership (Details) - shares	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Operating Partnership [Member]
General Partners' Capital Account [Abstract]
Ownership interest (percent)	99.00%	99.00%	98.40%
Kilroy Realty L.P. [Member] | Common units [Member]
General Partners' Capital Account [Abstract]
Company owned common units in the Operating Partnership (in units)	116,461,683	116,035,827	115,247,221
Noncontrolling common units of the Operating Partnership (in units)	1,150,574	1,150,574
Non-affiliated investors and certain of our executive officers and directors [Member] | Operating Partnership [Member]
General Partners' Capital Account [Abstract]
Ownership interest (percent)	1.00%	1.00%	1.60%
Non-affiliated investors and certain of our executive officers and directors [Member] | Common units [Member]
General Partners' Capital Account [Abstract]
Noncontrolling common units of the Operating Partnership (in units)	1,150,574	1,150,574	1,931,574