Goodwill and Other Acquired Intangible Assets - Schedule of Definite-Lived Intangible Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 75,337	$ 75,412
Accumulated Amortization	(54,950)	(53,251)
Net Carrying Amount	20,387	22,161
Core deposit intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	74,001	74,001
Accumulated Amortization	(53,887)	(52,165)
Net Carrying Amount	20,114	21,836
Customer relationship intangible asset
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,273	1,348
Accumulated Amortization	(1,036)	(1,064)
Net Carrying Amount	237	284
Non-compete agreement
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	63	63
Accumulated Amortization	(27)	(22)
Net Carrying Amount	$ 36	$ 41