Loans and the Allowance for Credit Losses - Recognition of Interest Income on Impaired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Receivables [Abstract]
Average impaired loans	$ 40,306	$ 39,623	$ 42,904
Amount of contractual interest income on impaired loans	3,047	2,631	3,089
Amount of interest income recognized on impaired loans	$ 341	$ 665	$ 722