Quarterly Financial Information of the Company (Unaudited) - Summarized Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 229,332	$ 228,314	$ 219,423	$ 221,328	$ 220,235	$ 215,525	$ 200,492	$ 201,202	$ 898,397	$ 837,454	$ 747,298
Net income	83,452	54,071	24,352	45,418	77,922	48,298	47,215	41,794	207,293	215,229	277,926
Net income attributable to Kilroy Realty Corporation	78,642	49,028	19,618	39,817	72,500	43,846	42,194	36,903
Net income available to common stockholders	$ 78,642	$ 49,028	$ 19,618	$ 39,817	$ 72,500	$ 43,846	$ 42,194	$ 36,903	$ 187,105	$ 195,443	$ 258,415
Net income available to common stockholders per share/ unit—basic (dollars per share/ unit)	$ 0.67	$ 0.42	$ 0.17	$ 0.37	$ 0.68	$ 0.41	$ 0.41	$ 0.36	$ 1.63	$ 1.87	$ 2.56
Net income available to common stockholders per share/ unit—diluted (dollars per share/ unit)	$ 0.67	$ 0.42	$ 0.17	$ 0.37	$ 0.67	$ 0.41	$ 0.41	$ 0.36	$ 1.63	$ 1.86	$ 2.55