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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Allowance for Covered Loan Losses [Roll Forward]
Balance at beginning of period	$ 1,074	$ 2,412	$ 1,322	$ 3,026
Provision for covered loan losses before benefit attributable to FDIC loss share agreements	(225)	(847)	(1,063)	(3,495)
Benefit attributable to FDIC loss share agreements	(180)	(677)	(850)	(2,796)
Net provision for covered loan losses	(45)	(170)	(213)	(699)
Increase in FDIC indemnification liability	(180)	(677)	(850)	(2,796)
Loans charged-off	(155)	(918)	(491)	(1,291)
Recoveries of loans charged-off	64	775	990	3,182
Net (charge-offs) recoveries	(91)	(143)	499	1,891
Balance at end of period	$ 758	$ 1,422	$ 758	$ 1,422