Related Party Transactions - Related Party Transactions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Gal-Tex Hotel Corporation | Mortgage Loan on Real Estate
Related Party Transaction [Line Items]
Dollar amount of transactions	$ 576	$ 1,647
Gal-Tex Hotel Corporation | Net Investment Income
Related Party Transaction [Line Items]
Dollar amount of transactions	9	107
Gal-Tex Hotel Corporation | Mortgage Loans on Real Estate
Related Party Transaction [Line Items]
Amount due to (from) American National	0	576
Gal-Tex Hotel Corporation | Net Investment Income
Related Party Transaction [Line Items]
Amount due to (from) American National	0	3
Greer, Herz & Adams, LLP | Other Operating Expenses
Related Party Transaction [Line Items]
Dollar amount of transactions	12,088	11,173
Greer, Herz & Adams, LLP | Other Operating Expenses
Related Party Transaction [Line Items]
Amount due to (from) American National	$ (519)	$ (329)