Loans and Allowance for Loan Losses - Summary of Troubled Debt Restructurings by Class of Loans, Payment Default (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Contract		Dec. 31, 2013 Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts	109		92
Recorded Investment	$ 945	[1]	$ 1,553	[1]
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts			1
Recorded Investment			737	[1]
Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts			1
Recorded Investment			12	[1]
Total Commercial Loans and Leases [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts			2
Recorded Investment			749	[1]
Direct Installment [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	97		76
Recorded Investment	728	[1]	380	[1]
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	4		7
Recorded Investment	151	[1]	303	[1]
Indirect Installment [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	7		6
Recorded Investment	16	[1]	36	[1]
Consumer Lines of Credit [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	1		1
Recorded Investment	$ 50	[1]	$ 85	[1]

[1] The recorded investment is as of period end.