Related Party Transactions - Related Party Transactions (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Gal-Tex Hotel Corporation | Mortgage loan on real estate
Related Party Transaction [Line Items]
Amount due to (from) American National	$ 0		$ 0
Gal-Tex Hotel Corporation | Net investment income
Related Party Transaction [Line Items]
Amount due to (from) American National	0		0
Gal-Tex Hotel Corporation | Mortgage loan on real estate
Related Party Transaction [Line Items]
Dollar Amount of Transactions	0	$ 431
Gal-Tex Hotel Corporation | Net investment income
Related Party Transaction [Line Items]
Dollar Amount of Transactions	0	8
Greer, Herz & Adams, LLP | Other operating expenses
Related Party Transaction [Line Items]
Amount due to (from) American National	(595)		$ (519)
Greer, Herz & Adams, LLP | Other operating expenses
Related Party Transaction [Line Items]
Dollar Amount of Transactions	$ 3,843	$ 2,889