Net Income Available to Common Unitholders Per Unit of the Operating Partnership - Basic and Diluted Net Income Per Share (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
Numerator:
Net income attributable to common unitholders									$ 187,105	$ 195,443	$ 258,415
Allocation to participating securities									(2,229)	(2,119)	(2,004)
Numerator for basic and diluted net income available to common stockholders									$ 184,876	$ 193,324	$ 256,411
Denominator:
Basic weighted average vested shares/units outstanding (in shares/units)									113,241,341	103,200,568	99,972,359
Effect of dilutive securities (in units)									478,281	648,600	510,006
Diluted weighted average vested shares and common stock/ unit equivalents outstanding (in shares/units)									113,719,622	103,849,168	100,482,365
Basic earnings per unit:
Net income available to common unitholders per unit - basic (in dollars per unit)	$ 0.67	$ 0.42	$ 0.17	$ 0.37	$ 0.68	$ 0.41	$ 0.41	$ 0.36	$ 1.63	$ 1.87	$ 2.56
Diluted earnings per unit:
Net income available to common unitholders per unit - diluted (in dollars per unit)	0.67	0.42	0.17	0.37	0.67	0.41	0.41	0.36	$ 1.63	$ 1.86	$ 2.55
Kilroy Realty L.P. [Member]
Numerator:
Net income attributable to common unitholders									$ 189,609	$ 198,738	$ 263,210
Allocation to participating securities									(2,229)	(2,119)	(2,004)
Numerator for basic and diluted net income available to common stockholders									$ 187,380	$ 196,619	$ 261,206
Denominator:
Basic weighted average vested shares/units outstanding (in shares/units)									115,095,506	105,223,975	102,025,276
Effect of dilutive securities (in units)									478,281	648,600	510,006
Diluted weighted average vested shares and common stock/ unit equivalents outstanding (in shares/units)									115,573,787	105,872,575	102,535,282
Basic earnings per unit:
Net income available to common unitholders per unit - basic (in dollars per unit)	0.67	0.42	0.16	0.37	0.68	0.41	0.41	0.36	$ 1.63	$ 1.87	$ 2.56
Diluted earnings per unit:
Net income available to common unitholders per unit - diluted (in dollars per unit)	$ 0.67	$ 0.42	$ 0.16	$ 0.36	$ 0.67	$ 0.41	$ 0.41	$ 0.36	$ 1.62	$ 1.86	$ 2.55