Loans - Summary of Impaired Financial Receivables (Summary of Covered Impaired Loans) (Detail) (USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 200,000
Troubled debt restructurings not included above	20,600,000	28,200,000	23,900,000
Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	88,939,000	151,225,000	115,712,000
Troubled debt restructurings not included above	22,709,000	14,842,000	19,194,000
Total impaired loans	111,648,000	166,067,000	134,906,000
Impaired loans not requiring a related allowance	111,648,000	166,067,000	134,906,000
Impaired loans requiring a related allowance
Allowance related to impaired loans
Average investment in impaired loans	122,220,000	178,130,000	163,825,000
Interest income recognized on impaired loans	784,000	628,000	849,000
Foregone interest income on impaired loans	$ 242,000	$ 482,000	$ 491,000