Short-Term Borrowings - Summary of Securities Pledged as Collateral Under Repurchase Agreements (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Offsetting Liabilities [Line Items]
Total securities pledged	$ 15,148	$ 28,925
Gross amount of recognized liabilities for repurchase agreements	15,148	28,925
Amounts related to agreements not included in offsetting disclosures above	0	0
U.S.Treasury Securities [Member]
Offsetting Liabilities [Line Items]
Total securities pledged	742	1,761
Obligations of U.S. Government Agencies [Member]
Offsetting Liabilities [Line Items]
Total securities pledged	$ 14,406	$ 27,164