Supplemental Financial Statement Information - Summary of Rollforward of Insurance Reserve (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Balance Sheet Components Disclosure [Abstract]
Beginning balance	$ 810,273	$ 376,538
Losses paid	(99,551)	(48,855)
Change in estimates	23,820	3,392
Reserves for current period	202,442	135,193
Ending balance	$ 936,984	$ 466,268