Loans - Summary of Impaired Financial Receivables Excluding Purchased Non-Covered and Covered Loans (Detail) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings not included above	$ 20,500,000	$ 20,200,000	$ 20,900,000
Excluding Purchased Non-Covered and Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	22,810,000	31,720,000	29,203,000
Troubled debt restructurings not included above	17,261,000	17,024,000	17,214,000
Total impaired loans	40,071,000	48,744,000	46,417,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Quarter-To-Date [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Quarter-to-date interest income recognized on impaired loans	117,000	17,000	54,000
Quarter-to-date foregone interest income on impaired loans	138,000	216,000	30,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Year-To-Date [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Quarter-to-date interest income recognized on impaired loans	799,000	468,000	522,000
Quarter-to-date foregone interest income on impaired loans	$ 161,000	$ 388,000	$ 418,000