Net Income Available to Common Stockholders Per Share of the Company - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income attributable to Kilroy Realty Corporation									$ 195,443	$ 258,415	$ 164,612
Preferred dividends and distributions									0	0	(13,363)
Allocation to participating securities									(2,119)	(2,004)	(1,975)
Numerator for basic and diluted net income available to common stockholders									$ 193,324	$ 256,411	$ 149,274
Denominator:
Basic weighted average vested shares/units outstanding (in shares/units)									103,200,568	99,972,359	98,113,561
Effect of dilutive securities (in shares)									648,600	510,006	613,770
Diluted weighted average vested shares and common stock/ unit equivalents outstanding (in shares/units)									103,849,168	100,482,365	98,727,331
Basic earnings per share:
Net income available to common stockholders per share - basic (in dollars per share)	$ 0.68	$ 0.41	$ 0.41	$ 0.36	$ 1.59	$ 0.34	$ 0.27	$ 0.36	$ 1.87	$ 2.56	$ 1.52
Diluted earnings per share:
Net income available to common stockholders per share - diluted (in dollars per share)	$ 0.67	$ 0.41	$ 0.41	$ 0.36	$ 1.58	$ 0.33	$ 0.27	$ 0.36	$ 1.86	$ 2.55	$ 1.51