Loans and Allowance for Loan Losses - Summary of Impaired Financial Receivables (Summary of Non-Covered Impaired Loans) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Finance Receivable Transferred To Held For Sale [Line Items]
Nonaccrual loans		$ 200,000
Troubled debt restructurings not included above	23,900,000	26,100,000
Non-Covered Loan [Member]
Finance Receivable Transferred To Held For Sale [Line Items]
Nonaccrual loans	38,885,000	70,823,000	79,289,000	96,131,000	65,414,000
Troubled debt restructurings not included above	18,744,000	17,951,000	21,972,000
Total impaired loans	57,629,000	88,774,000	101,261,000
Impaired loans not requiring a related allowance
Impaired loans requiring a related allowance	57,629,000	88,774,000	101,261,000
Allowance related to impaired loans	5,115,000	18,478,000	16,688,000
Average investment in impaired loans	70,209,000	88,320,000	103,776,000
Interest income recognized on impaired loans	495,000	637,000	545,000
Foregone interest income on impaired loans	$ 718,000	$ 613,000	$ 3,828,000