Allowance for Loan Losses - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Contracts	Dec. 31, 2013 Contracts
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of troubled debt restructurings	2	7
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Troubled debt restructurings, subsequently defaulted	2,191,000	6,000
Financing allowance increase in principal		5,246
Number of troubled debt restructurings	1	3
Financing allowance reduction in interest payments		23,227
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing allowance increase in principal	100
Number of troubled debt restructurings	2	2
Financing allowance reduction in principal		808
Financing allowance reduction in interest payments		606
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of troubled debt restructurings		1
Financing allowance reduction in principal		1,515
Financing allowance reduction in interest payments		1,098
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of troubled debt restructurings		1
Financing allowance reduction in principal		4,704
Financing allowance reduction in interest payments		4,104