Loans and Allowance for Loan Losses - Summary of Impaired Financial Receivables Excluding Purchased Non-Covered and Covered Loans (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings not included above	$ 1,214,000	$ 3,390,000
Excluding Purchased Non-Covered and Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	21,728,000	29,203,000	38,885,000
Troubled debt restructurings not included above	12,759,000	17,214,000	18,744,000
Total impaired loans	34,487,000	46,417,000	57,629,000
Interest income recognized on impaired loans	1,170,000	522,000	495,000
Foregone interest income on impaired loans	$ 155,000	$ 418,000	$ 718,000