Schedule II. Condensed Financial Information of Registrant - Condensed Balance Sheets (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Condensed Balance Sheet Statements, Captions [Line Items]
Fixed maturity securities, held-to-maturity, allowance for credit losses	$ 274	$ 0
Fixed maturity securities, fair value	621,654	621,343
Fixed maturity securities, amortized cost	387,665	425,698
Equity securities, cost	35,787	24,457
Net of Treasury stock	22,370	22,370
Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Fixed maturity securities, held-to-maturity, allowance for credit losses	0	0
Fixed maturity securities, fair value	361	0
Fixed maturity securities, amortized cost	7,210	7,210
Equity securities, cost	10,007	10,007
Net of Treasury stock	$ 22,370	$ 22,370