Short-term Borrowings - Interest Expense on Short-Term Borrowings (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	$ 8,076	$ 5,018	$ 2,449
Federal funds purchased
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	41	54	42
Borrowings from FHLB
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	7,765	4,684	2,019
Securities sold under agreements to repurchase
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	$ 270	$ 280	$ 388