Investment Securities - Summary of Available for Sale Securities (Parenthetical) (Detail) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
Dec. 31, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Impairment charge other-than-temporary impairments	$ 60,000	$ 0	$ 0	$ 60,000

This element represents the amount of loss recognized for other than temporary impairments (OTTI) of investments in debt and equity securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 5.M)
-URI http://asc.fasb.org/extlink&oid=65877573&loc=d3e87990-122713

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