Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 31,994	$ 32,003
Accumulated Amortization	(17,058)	(15,533)
Net Carrying Amount	14,936	16,470
Core Deposit Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	25,907	25,907
Accumulated Amortization	(12,456)	(11,113)
Net Carrying Amount	13,451	14,794
Customer Relationship Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,699	5,699
Accumulated Amortization	(4,289)	(4,115)
Net Carrying Amount	1,410	1,584
Mortgage Servicing Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	388	397
Accumulated Amortization	(313)	(305)
Net Carrying Amount	$ 75	$ 92