Loans and Allowance for Credit Losses - Schedule of Loans by Class Modified as Troubled Debt Restructuring (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 SecurityLoan	Mar. 31, 2014 SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans	29	21
Pre-modification Outstanding Recorded Investment	$ 3,840	$ 1,234
Post-modification Outstanding Recorded Investment	3,840	1,234
Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	11	7
Pre-modification Outstanding Recorded Investment	1,741	188
Post-modification Outstanding Recorded Investment	1,741	188
Commercial Real Estate - Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	5	1
Pre-modification Outstanding Recorded Investment	1,187	484
Post-modification Outstanding Recorded Investment	1,187	484
Commercial Real Estate - Other [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	5	3
Pre-modification Outstanding Recorded Investment	385	246
Post-modification Outstanding Recorded Investment	385	246
Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	2	1
Pre-modification Outstanding Recorded Investment	366	22
Post-modification Outstanding Recorded Investment	366	22
Consumer - Other [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	6	9
Pre-modification Outstanding Recorded Investment	161	294
Post-modification Outstanding Recorded Investment	$ 161	$ 294