Securities - Additional Information (Detail) $ in Thousands	Jun. 30, 2018 USD ($) Security	Dec. 31, 2017 USD ($)
Investments Debt And Equity Securities [Abstract]
Carrying value of pledged securities \| $	$ 130,506	$ 122,862
Number of securities in portfolio with unrealized losses \| Security	130

Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

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