Loans - Summary of Impaired Financial Receivables (Summary of Non-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
Non-Covered Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	31,811,000	44,421,000	38,885,000
Troubled debt restructurings not included above	18,015,000	22,970,000	18,744,000
Total impaired loans	49,826,000	67,391,000	57,629,000
Impaired loans not requiring a related allowance
Impaired loans requiring a related allowance	49,826,000	67,391,000	57,629,000
Allowance related to impaired loans	5,072,000	7,136,000	5,115,000
Average investment in impaired loans	54,481,000	78,432,000	70,209,000
Interest income recognized on impaired loans	451,000	153,000	495,000
Foregone interest income on impaired loans	$ 172,000	$ 332,000	$ 718,000