Commitments and Contingencies - Additional Information (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) shares
Conversion of Stock [Line Items]
Reserves to satisfy Federal regulatory requirements | $		$ 136,370
Letters of credit, issue period	one year
Common stock, shares outstanding (in shares) | shares	29,727,214	30,523,824
Conversion ratio	1.6228
Common Class B
Conversion of Stock [Line Items]
Common stock, shares outstanding (in shares) | shares	13,396
Common Class A
Conversion of Stock [Line Items]
The value of the Class A shares | $ / shares	$ 218.73
Value of unredeemed Class A equivalent shares | $	$ 4,755