Loans - Summary of Impaired Financial Receivables (Summary of 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
Covered Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	39,283,000	74,911,000	69,152,000
Troubled debt restructurings not included above	22,757,000	21,184,000	22,243,000
Total impaired loans	62,040,000	96,095,000	91,395,000
Covered Impaired Loans [Member] | Quarter-To-Date [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Quarter-to-date interest income recognized on impaired loans	176,000	9,000	175,000
Quarter-to-date foregone interest income on impaired loans	0	44,000	44,000
Covered Impaired Loans [Member] | Year-To-Date [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Quarter-to-date interest income recognized on impaired loans	1,115,000	793,000	968,000
Quarter-to-date foregone interest income on impaired loans	$ 94,000	$ 286,000	$ 330,000