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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income attributable to Kilroy Realty, L.P.									$ 258,415	$ 164,612	$ 293,788
Preferred dividends and distributions					$ 0	$ (4,552)	$ (1,615)	$ (7,196)	0	(13,363)	(13,250)
Allocation to participating securities (1)									(2,004)	(1,975)	(3,839)
Numerator for basic and diluted net income available to common stockholders									$ 256,411	$ 149,274	$ 276,699
Denominator:
Basic weighted average vested shares/units outstanding (in shares/units)									99,972,359	98,113,561	92,342,483
Effect of dilutive securities (in units)									510,006	613,770	680,551
Diluted weighted average vested shares and common stock/ unit equivalents outstanding (in shares/units)									100,482,365	98,727,331	93,023,034
Basic earnings per unit:
Net income available to common unitholders per unit (in dollars per unit)	$ 1.59	$ 0.34	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.27	$ 2.56	$ 1.52	$ 3.00
Diluted earnings per unit:
Net income available to common unitholders per unit (in dollars per unit)	1.58	0.33	0.27	0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.26	$ 2.55	$ 1.51	$ 2.97
Kilroy Realty L.P. [Member]
Numerator:
Net income attributable to Kilroy Realty, L.P.									$ 263,210	$ 167,440	$ 300,063
Preferred dividends and distributions					$ 0	$ (4,552)	$ (1,615)	$ (7,196)	0	(13,363)	(13,250)
Allocation to participating securities (1)									(2,004)	(1,975)	(3,839)
Numerator for basic and diluted net income available to common stockholders									$ 261,206	$ 152,102	$ 282,974
Denominator:
Basic weighted average vested shares/units outstanding (in shares/units)									102,025,276	100,246,567	94,771,688
Effect of dilutive securities (in units)									510,006	613,770	680,551
Diluted weighted average vested shares and common stock/ unit equivalents outstanding (in shares/units)									102,535,282	100,860,337	95,452,239
Basic earnings per unit:
Net income available to common unitholders per unit (in dollars per unit)	1.58	0.34	0.27	0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.26	$ 2.56	$ 1.52	$ 2.99
Diluted earnings per unit:
Net income available to common unitholders per unit (in dollars per unit)	$ 1.57	$ 0.33	$ 0.27	$ 0.36	$ 0.28	$ 0.67	$ 0.30	$ 0.26	$ 2.55	$ 1.51	$ 2.96