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Goodwill and Other Amortizing Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill And Other Intangibles [Line Items]
Goodwill	$ 274,202,000	$ 255,353,000
Goodwill, Acquired During Period	18,800,000
Impairment charges on goodwill	0	0	$ 0
Servicing Asset	500,000	100,000
Total amortization	9,946,000	6,822,000
Intangible amortization	$ 3,217,000	3,081,000	547,000
Customer deposit intangibles
Goodwill And Other Intangibles [Line Items]
Core deposits remaining amortization period	9 years 4 months
Core deposits weighted average amortization period	8 years
Total amortization	$ 8,877,000	6,071,000
Customer list intangible
Goodwill And Other Intangibles [Line Items]
Core deposits remaining amortization period	10 years 8 months
Core deposits weighted average amortization period	8 years 11 months
Total amortization	$ 1,069,000	751,000
Customer-Related Intangible Assets [Member]
Goodwill And Other Intangibles [Line Items]
Intangible amortization	$ 3,124,000	$ 3,081,000	$ 547,000

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Finite Lived Intangible Asset Remaining Amortization Period

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Goodwill And Other Intangibles [Line Items]

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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Aggregate amount of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method.

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