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Investments - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2020 USD ($) Security	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Marketable Securities [Line Items]
Individual fixed maturity held in unrealized loss position | Security	20
Individual fixed maturity held in unrealized loss position longer than 12 months | Security	0
Number of fixed maturity securities, allowance for credit loss | Security	419
Fixed maturity securities, allowance for credit loss	$ 275,000		$ 0
Fixed maturity securities, available-for-sale, allowance for credit losses	0		$ 0
Net realized gains	1,000,000.0
Net unrealized gains (losses) on equity securities	(8,763,000)	$ 2,158,000
Corporate Bonds [Member]
Marketable Securities [Line Items]
Fixed maturity securities, allowance for credit loss	$ 215,000
Number of majority securities | Security	48
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Fixed maturity securities, allowance for credit loss	$ 50,000
Number of majority securities | Security	368
Corporate Fixed Income Securities [Member] | Maximum [Member]
Marketable Securities [Line Items]
Investments maturity period using default rate	20 years

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