Quarterly Financial Information of the Operating Partnership (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues	$ 168,645	$ 168,348	$ 160,133	$ 145,446	$ 147,413	$ 141,553	$ 146,227	$ 146,082	$ 642,572	$ 581,275	$ 521,725
Net income	35,418	56,375	33,892	178,113	29,308	106,704	58,590	44,002	303,798	238,604	183,808
Net income attributable to the Operating Partnership	32,738	53,895	32,847	174,308	28,635	104,759	57,500	43,187	293,788	234,081	180,219
Preferred distributions	(3,312)	(3,313)	(3,312)	(3,313)	(3,312)	(3,313)	(3,312)	(3,313)	(13,250)	(13,250)	(13,250)
Net income available to common stockholders	$ 29,426	$ 50,582	$ 29,535	$ 170,995	$ 25,323	$ 101,446	$ 54,188	$ 39,874	$ 280,538	$ 220,831	$ 166,969
Net income (loss) available to common stockholders per share—basic (dollars per share)	$ 0.29	$ 0.54	$ 0.32	$ 1.85	$ 0.27	$ 1.10	$ 0.61	$ 0.45	$ 3.00	$ 2.44	$ 1.99
Net income (loss) available to common stockholders per share—diluted (dollars per share)	$ 0.29	$ 0.54	$ 0.31	$ 1.84	$ 0.27	$ 1.09	$ 0.61	$ 0.45	$ 2.97	$ 2.42	$ 1.95
Kilroy Realty, L.P. [Member]
Revenues	$ 168,645	$ 168,348	$ 160,133	$ 145,446	$ 147,413	$ 141,553	$ 146,227	$ 146,082	$ 642,572	$ 581,275	$ 521,725
Net income	35,418	56,375	33,892	178,113	29,308	106,704	58,590	44,002	303,798	238,604	183,808
Net income attributable to the Operating Partnership	33,386	55,254	33,590	177,833	29,052	106,640	58,518	43,927	300,063	238,137	183,548
Preferred distributions	(3,312)	(3,313)	(3,312)	(3,313)	(3,312)	(3,313)	(3,312)	(3,313)	(13,250)	(13,250)	(13,250)
Net income available to common stockholders	$ 30,074	$ 51,941	$ 30,278	$ 174,520	$ 25,740	$ 103,327	$ 55,206	$ 40,614	$ 286,813	$ 224,887	$ 170,298
Net income (loss) available to common stockholders per share—basic (dollars per share)	$ 0.29	$ 0.54	$ 0.31	$ 1.85	$ 0.27	$ 1.10	$ 0.61	$ 0.45	$ 2.99	$ 2.44	$ 1.99
Net income (loss) available to common stockholders per share—diluted (dollars per share)	$ 0.29	$ 0.54	$ 0.31	$ 1.84	$ 0.27	$ 1.09	$ 0.61	$ 0.45	$ 2.96	$ 2.42	$ 1.94