Loans - Summary of Impaired Financial Receivables (Summary of 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
Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	74,911,000	123,901,000	115,712,000
Troubled debt restructurings not included above	21,184,000	25,926,000	19,194,000
Total impaired loans	96,095,000	149,827,000	134,906,000
Impaired loans not requiring a related allowance	96,095,000	149,827,000	134,906,000
Impaired loans requiring a related allowance
Allowance related to impaired loans
Average investment in impaired loans	115,689,000	171,055,000	163,825,000
Interest income recognized on impaired loans	793,000	1,319,000	849,000
Foregone interest income on impaired loans	$ 286,000	$ 554,000	$ 491,000