Related Party Transactions - Related Party Transactions (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Gal-Tex Hotel Corporation | Mortgage loan on real estate
Related Party Transaction [Line Items]
Dollar Amount of Transactions	$ 576	$ 1,224
Gal-Tex Hotel Corporation | Net investment income
Related Party Transaction [Line Items]
Dollar Amount of Transactions	9	92
Gal-Tex Hotel Corporation | Mortgage loan 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	9,025	$ 8,008
Greer, Herz & Adams, LLP | Other operating expenses
Related Party Transaction [Line Items]
Amount due to (from) American National	$ (560)		$ (329)