Short-term Borrowings - Interest Expense on Short-Term Borrowings (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	$ 2,449	$ 1,262	$ 1,070
Federal funds purchased [Member]
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	42	43	128
Borrowings from FHLB [Member]
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	2,019	893	545
Securities sold under agreements to repurchase [Member]
Interest On Short Term Borrowings [Line Items]
Total interest on short-term borrowings	$ 388	$ 326	$ 397