Goodwill and Other Intangible Assets - Summary of Core Deposit Intangibles (Detail) - Core Deposit Intangibles [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Finite-Lived Intangible Assets [Line Items]
Core deposit intangibles, Beginning balance	$ 10,120
Core deposit intangibles, Fully Depreciated	(562)
Core deposit intangibles, Reductions/Amortization	0
Core deposit intangibles, Additions	0
Core deposit intangibles, Ending balance	9,558
Accumulated amortization, Beginning balance	(3,557)
Accumulated amortization, Fully Depreciated	562
Accumulated amortization, Reductions/Amortization	(1,389)
Accumulated amortization, Additions	0
Accumulated amortization, Ending balance	(4,384)
Core deposit intangibles, net, Beginning balance	6,563
Core deposit intangibles, net, Fully Depreciated	0
Core deposit intangibles, net, Reductions/Amortization	(1,389)
Core deposit intangibles, net, Additions	0
Core deposit intangibles, net, Ending balance	$ 5,174