Federal Income Taxes - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Tax Credit Carryforward [Line Items]
Income taxes paid or refunded, net	$ 40,440,000	$ 14,135,000
Income tax examination description	American National’s federal income tax returns for years 2015 to 2017 are subject to examination by the Internal Revenue Service.
AMT Credit Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforward	$ 6,933,000
General Business Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforward	758,000
Capital Loss Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforward	$ 656,000