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Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)		12 Months Ended
	Aug. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill impairment	$ 0
Impairment charges		$ 0	$ 0	$ 0
Amortization of other intangible assets		$ 14,091,000	$ 16,911,000	$ 14,442,000
Core Deposits and Other Intangible Assets | Minimum
Goodwill [Line Items]
Estimated useful lives of core deposits and customer relationships		5 years
Core Deposits and Other Intangible Assets | Maximum
Goodwill [Line Items]
Estimated useful lives of core deposits and customer relationships		15 years

X

- Definition

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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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of impairment loss resulting from write-down of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit to fair value.

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