Allowance for Loan Losses - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Evaluation for impairment of substandard and nonaccrual commercial loans	500,000
Total amount of all impaired loans	43,977,000	52,856,000
Commercial real estate impaired loans current appraisals	0
Commercial real estate impaired loans needing current appraisals	0
Minimum [Member]
Financing Receivable, Impaired [Line Items]
Loans considered nonperforming (in days)	90 days
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total amount of all impaired loans	19,890,000	$ 26,968,000