Securities Available for Sale - Summary of Proceeds from Sales of Securities Available-for-sale, as well as Gross Gains and Losses (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales of securities available-for-sale	$ 4,875	$ 14,392
Gross realized gains	$ 46	137
Gross realized losses		$ 70

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26853-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

Name:	us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration