Supplemental Financial Statement Information - Summary of Rollforward of Insurance Reserve (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Insurance Reserves [Roll Forward]
Beginning balance	$ 1,378,462	$ 810,273
Losses paid	(430,429)	(349,919)
Change in estimates for prior periods	61,248	198,348
Transfer of certain legacy auto insurance liabilities	(407,885)	0
Reserves for current period	321,232	716,233
Ending balance	$ 922,628	$ 1,374,935