Covered Loans - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Covered Loans [Line Items]
Covered loans	$ 250,801,000	$ 372,333,000	$ 448,789,000
Outstanding covered loans including principal, interest, fees and penalties	388,900,000	529,200,000
Percentage of prospective yield adjustments offset	80.00%
Loss sharing asset	91,600,000
Loss sharing asset, FDIC indemnification asset	81,600,000
Loss sharing asset, loss share receivable	10,000,000
Percentage of increase in indemnification asset measured as a result of impairment	80.00%
Expected Indemnification Payments [Member]
Covered Loans [Line Items]
Loss sharing asset, FDIC indemnification asset	50,600,000
To Be Amortized Against Future Accreted Interest Income [Member]
Covered Loans [Line Items]
Loss sharing asset, FDIC indemnification asset	$ 31,000,000