Loans - Summary of Impaired Financial Receivables (Summary of Purchased Non-Covered Impaired 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
Purchased Non-Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	17,007,000		6,659,000
Troubled debt restructurings not included above	583,000		0
Total impaired loans	17,590,000		6,659,000
Purchased Non-Covered Loans [Member] | Quarter-To-Date [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Quarter-to-date interest income recognized on impaired loans	19,000		0
Quarter-to-date foregone interest income on impaired loans	18,000		0
Purchased Non-Covered Loans [Member] | Year-To-Date [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Quarter-to-date interest income recognized on impaired loans	35,000		0
Quarter-to-date foregone interest income on impaired loans	$ 176,000		$ 0