Goodwill and Other Intangible Assets - Components of Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 37,193	$ 35,734
Accumulated Amortization and Fair Value Adjustments	25,203	21,825
Net Carrying Amount	11,990	13,909
Covenants Not To Compete [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	710	710
Accumulated Amortization and Fair Value Adjustments	710	580
Net Carrying Amount	0	130
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,788	6,788
Accumulated Amortization and Fair Value Adjustments	3,143	2,135
Net Carrying Amount	3,645	4,653
Customer Related Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	12,381	12,381
Accumulated Amortization and Fair Value Adjustments	10,804	9,828
Net Carrying Amount	1,577	2,553
Servicing Rights [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	17,314	15,855
Accumulated Amortization and Fair Value Adjustments	10,546	9,282
Net Carrying Amount	$ 6,768	$ 6,573