Investment Securities - Proceeds from Sale, Gross Gains (Losses) Realized on Sales, Maturities and Other-Than-Temporary Impairment Charges Related to Securities Available for Sale (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Gain (Loss) on Securities [Line Items]
Proceeds from sale	$ 948	$ 15,939	$ 143,660
Net gains (losses) and impairment	22	8,102	5,040
Calls And Maturities [Member]
Gain (Loss) on Securities [Line Items]
Gross losses	0	0	(60)
Gross gains	29	3,383	5,057
Other-than-temporary impairment	0	0	0
Total gain (losses) maturities and impairment	29	3,383	4,997
Sales [Member]
Gain (Loss) on Securities [Line Items]
Gross losses	(7)	0	(316)
Available-for-sale Securities, Gross Realized Losses	0	4,719	359
Total gain (losses) from sales transactions	$ (7)	$ 4,719	$ 43