Goodwill and Other Intangible Assets - Schedule of Definite-Lived Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 75,207	$ 75,412
Accumulated Amortization	(56,474)	(53,251)
Net Carrying Amount	18,733	22,161
Core deposit intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	74,001	74,001
Accumulated Amortization	(55,501)	(52,165)
Net Carrying Amount	18,500	21,836
Customer relationship intangible asset
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,143	1,348
Accumulated Amortization	(942)	(1,064)
Net Carrying Amount	201	284
Non-compete agreement
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	63	63
Accumulated Amortization	(31)	(22)
Net Carrying Amount	$ 32	$ 41