Securities - Additional Information (Detail) $ in Thousands	Dec. 31, 2017 USD ($) Security	Dec. 31, 2016 USD ($)
Investments Debt And Equity Securities [Abstract]
Carrying value of pledged securities \| $	$ 122,862	$ 139,179
Number of securities in portfolio with unrealized losses \| Security	78

The fair value of available-for-sale securities that serve as collateral for borrowings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

Name:	us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant