Goodwill and Other Intangible Assets - Components of Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 35,734	$ 34,248
Accumulated Amortization and Fair Value Adjustments	21,825	17,597
Net Carrying Amount	13,909	16,651
Covenants Not To Compete [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	710	710
Accumulated Amortization and Fair Value Adjustments	580	205
Net Carrying Amount	130	505
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,788	6,788
Accumulated Amortization and Fair Value Adjustments	2,135	1,004
Net Carrying Amount	4,653	5,784
Customer Related Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	12,381	12,381
Accumulated Amortization and Fair Value Adjustments	9,828	8,504
Net Carrying Amount	2,553	3,877
Servicing Rights [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	15,855	14,369
Accumulated Amortization and Fair Value Adjustments	9,282	7,884
Net Carrying Amount	$ 6,573	$ 6,485