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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Allowance for Covered Loan Losses [Roll Forward]
Balance at beginning of period	$ 1,319	$ 2,507	$ 1,322	$ 3,026
Provision for covered loan losses before benefit attributable to FDIC loss share agreements	(303)	(702)	(838)	(2,648)
Benefit attributable to FDIC loss share agreements	242	562	670	2,119
Net provision for covered loan losses	(61)	(140)	(168)	(529)
Increase/decrease in FDIC indemnification liability/asset	(242)	(562)	(670)	(2,119)
Loans charged-off	(120)	(143)	(336)	(373)
Recoveries of loans charged-off	178	750	926	2,407
Net recoveries	58	607	590	2,034
Balance at end of period	$ 1,074	$ 2,412	$ 1,074	$ 2,412