Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Summary of Activity in the Allowance for Covered Loan Losses) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Allowance for Covered Loan Losses [Roll Forward]
Balance at beginning of period	$ 2,215	$ 1,667	$ 2,131	$ 10,092
Provision for covered loan losses before benefit attributable to FDIC loss share agreements	(1,716)	(818)	(3,339)	(8,703)
Benefit attributable to FDIC loss share agreements	1,373	654	2,671	6,962
Net provision for covered loan losses	(343)	(164)	(668)	(1,741)
Decrease in FDIC indemnification asset	(1,373)	(654)	(2,671)	(6,962)
Loans charged-off	(287)	(293)	(664)	(5,346)
Recoveries of loans charged-off	2,706	2,099	4,790	6,612
Net recoveries (charge-offs)	2,419	1,806	4,126	1,266
Balance at end of period	$ 2,918	$ 2,655	$ 2,918	$ 2,655