Goodwill and Other Intangible Assets (Schedule of Other Intangible Assets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	$ 14,043	$ 15,476
Accumulated Amortization	(8,970)	(8,700)
Net Intangible Assets	5,073	6,776
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	9,300	9,300
Accumulated Amortization	(5,256)	(4,002)
Net Intangible Assets	4,044	5,298
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	4,669	6,102
Accumulated Amortization	(3,683)	(4,692)
Net Intangible Assets	986	1,410
Noncompete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	74	74
Accumulated Amortization	(31)	(6)
Net Intangible Assets	$ 43	$ 68