Short-term Borrowings - Interest Expense on Short-Term Borrowings (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	$ 704	$ 8,298	$ 10,741
Federal funds purchased
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	44	204	180
Borrowings from FHLB
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	434	7,313	9,929
Securities sold under agreements to repurchase
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	$ 226	$ 781	$ 632