Loans - Summary of Impaired Financial Receivables (Summary of Non-Covered Impaired Loans) (Detail) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 200,000
Troubled debt restructurings not included above	20,200,000	23,300,000	23,900,000
Non-Covered Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	31,720,000	38,225,000	38,885,000
Troubled debt restructurings not included above	17,024,000	19,893,000	18,744,000
Total impaired loans	48,744,000	58,118,000	57,629,000
Impaired loans not requiring a related allowance
Impaired loans requiring a related allowance	48,744,000	58,118,000	57,629,000
Allowance related to impaired loans	5,180,000	7,681,000	5,115,000
Average investment in impaired loans	53,047,000	73,353,000	70,209,000
Interest income recognized on impaired loans	468,000	376,000	495,000
Foregone interest income on impaired loans	$ 388,000	$ 491,000	$ 718,000