Net Income Available to Common Unitholders Per Unit of the Operating Partnership (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income attributable to Kilroy Realty, L.P.	$ 34,400	$ 71,110	$ 98,195	$ 136,083
Total preferred dividends	0	(4,552)	0	(13,363)
Allocation to participating securities	(507)	(501)	(1,492)	(1,460)
Numerator for basic and diluted net income available to common stockholders	$ 33,893	$ 66,057	$ 96,703	$ 121,260
Denominator:
Basic weighted average vested shares outstanding (in shares)	100,676,778	98,352,139	99,711,312	98,008,780
Effect of dilutive securities (in units)	551,556	559,473	497,333	582,268
Diluted weighted average vested shares and common share equivalents outstanding (in shares)	101,228,334	98,911,612	100,208,645	98,591,048
Basic earnings per unit:
Net income available to common stockholders per share (in dollars per share)	$ 0.34	$ 0.67	$ 0.97	$ 1.24
Diluted earnings per unit:
Net income available to common stockholders per share (in dollars per share)	$ 0.33	$ 0.67	$ 0.97	$ 1.23
Kilroy Realty L.P. [Member]
Numerator:
Net income attributable to Kilroy Realty, L.P.	$ 34,993	$ 72,402	$ 99,901	$ 138,427
Total preferred dividends	0	(4,552)	0	(13,363)
Allocation to participating securities	(507)	(501)	(1,492)	(1,460)
Numerator for basic and diluted net income available to common stockholders	$ 34,486	$ 67,349	$ 98,409	$ 123,604
Denominator:
Basic weighted average vested shares outstanding (in shares)	102,721,806	100,429,332	101,773,540	100,160,595
Effect of dilutive securities (in units)	551,556	559,473	497,333	582,268
Diluted weighted average vested shares and common share equivalents outstanding (in shares)	103,273,362	100,988,805	102,270,873	100,742,863
Basic earnings per unit:
Net income available to common stockholders per share (in dollars per share)	$ 0.34	$ 0.67	$ 0.97	$ 1.23
Diluted earnings per unit:
Net income available to common stockholders per share (in dollars per share)	$ 0.33	$ 0.67	$ 0.96	$ 1.23