Short-Term Borrowings - Summary of Repurchase Agreements Accounted for as Secured Borrowings (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Short-term Debt [Abstract]
Securities of U.S. Government Agencies and mortgage-backed securities of government agencies pledged, fair value	$ 44,343	$ 39,637
Repurchase agreements	$ 44,155	$ 39,480

Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Name:	us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant