Loans - Schedule of Modified TDRs (Detail) - Troubled Debt Restructurings [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Modifications
TDRs during period on accrual status	$ 12,900	$ 11,800
TDRs during period on non-accrual status	14,300	1,400
Extended maturities	5,619	7,199
Maturity and interest rate adjustment	108	3,224
Movement to or extension of interest-rate only payments	48	1,290
Interest rate adjustment	105	0
Financing Receivable Modifications Forbearance	12,886	1,220
Other concession(s)	8,434	232
TDRs during period	$ 27,200	$ 13,165