Summary of Significant Accounting Policies - Summary of Deferred Policy Acquisition Cost Amortization and Net Advertising Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Deferred policy acquisition cost amortization	$ 627,788	$ 602,085	$ 572,164
Net advertising expense	$ 37,700	$ 42,200	$ 40,900