Goodwill and Other Intangible Assets - Summary of Core Deposit Intangibles (Detail) - Core Deposit Intangibles [Member] $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Finite-Lived Intangible Assets [Line Items]
Core deposit intangibles, Beginning balance	$ 9,558
Core deposit intangibles, Reductions/Amortization	0
Core deposit intangibles, Additions	0
Core deposit intangibles, Ending balance	9,558
Accumulated amortization, Beginning balance	(4,384)
Accumulated amortization, Reductions/Amortization	(339)
Accumulated amortization, Additions	0
Accumulated amortization, Ending balance	(4,723)
Core deposit intangibles, net, Beginning balance	5,174
Core deposit intangibles, net, Reductions/Amortization	(339)
Core deposit intangibles, net, Additions	0
Core deposit intangibles, net, Ending balance	$ 4,835