Acquisition and Divestiture Activity - Additional Information (Detail) - KleinBank [Member] - Minnesota [Member] shares in Millions, $ in Millions	Nov. 01, 2018 USD ($) Branch shares
Business Acquisition [Line Items]
Stock merger acquisition ratio	100.00%
Number of branches \| Branch	18
Portion of share received by merged entity	7.92
Total fair value of consideration paid	$ 406.5
Issuance of common stock shares for acquisitions of business \| shares	22.8
Value of issuance common stock shares	$ 406.5
Transaction and integration costs associated with the acquisition	18.8
Core Deposit [Member]
Business Acquisition [Line Items]
Estimated fair value of intangible assets acquired	$ 39.0
Estimated useful life of intangible assets	12 years

Business combination equity interest exchange ratio.

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Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Value of equity interests (such as common shares, preferred shares, or partnership interest) issued or issuable to acquire the entity.

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Number of shares of equity interests issued or issuable to acquire entity.

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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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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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- Definition

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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Amount recognized for assets, including goodwill, in excess of (less than) the aggregate liabilities assumed.

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- Definition

Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, from an acquisition.

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- Definition

Represents the number of stores.

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