Business Combinations - Summary of Consideration Paid and Fair Value of Identifiable Assets Acquired and Liabilities Assumed (Parenthetical) (Detail) - shares	Sep. 05, 2014	Nov. 25, 2013
First Wyoming Financial Corporation [Member]
Business Acquisition [Line Items]
Common stock shares issued	1,357,983	1,357,983

Number of shares of equity interests issued or issuable to acquire entity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (b)(4)

-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Name:	us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration