Short-Term Borrowings - Summary of Securities Pledged as Collateral Under Repurchase Agreements (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Offsetting Liabilities [Line Items]
Total securities pledged	$ 14,230	$ 21,755
Gross amount of recognized liabilities for repurchase agreements	14,230	21,755
Amounts related to agreements not included in offsetting disclosures above	0	0
U.S.Treasury Securities [Member]
Offsetting Liabilities [Line Items]
Total securities pledged	632	874
Obligations of U.S. Government Agencies [Member]
Offsetting Liabilities [Line Items]
Total securities pledged	$ 13,598	$ 20,881