CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	280,000,000	280,000,000
Common stock, shares issued (in shares)	116,461,683	116,035,827
Common stock, shares outstanding (in shares)	116,461,683	116,035,827
Common units [Member] | Kilroy Realty L.P. [Member]
General partner, units issued	116,461,683	116,035,827
General partners, units outstanding	116,461,683	116,035,827
Limited partners, units issued	1,150,574	1,150,574
Limited partners, units outstanding	1,150,574	1,150,574