Business Combination, Acquired Receivables, Increase Decrease

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Shares transferred at acquisition-date in consideration of business combination.

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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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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 consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of equity interests of the acquirer, including instruments or interests issued or issuable in consideration for the business combination.

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The amount of property, plant, and equipment recognized as of the acquisition date.

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

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Number of shares of stock issued during the period pursuant to acquisitions.

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Acquisitions - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
Acquisitions - Narrative (Details) - USD ($) $ in Thousands	Feb. 01, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Approximate value of stock transaction					$ 488,408	$ 0
Bank Mutual
Business Acquisition [Line Items]
Number of shares received by shareholders (in shares)	0.422
Approximate number of shares issued	19,500,000
Approximate value of stock transaction	$ 482,000
Goodwill acquired	$ 175,000
Amortization period	10 years
Approximate additions to finite-lived intangible assets	$ 58,000
BKMU Goodwill Acquired Adjustments
Business Acquisition [Line Items]
Goodwill acquired		$ 2,000	$ 6,000
BKMU Assets Acquired Liabilities Assumed IncreaseDecrease
Business Acquisition [Line Items]
Updated appraisal information, fair value or premises and equipment		$ 2,000	6,000		$ 2,000
Updated appraisal and other adjustments, fair value of loans	less than $1 million
Anderson Insurance Investment Agency
Business Acquisition [Line Items]
Goodwill acquired			$ 7,000
Amortization period			7 years
Approximate value of acquisition			$ 10,000
Approximate additions to finite-lived intangible assets			$ 3,000
Diversified Insurance Solutions
Business Acquisition [Line Items]
Goodwill acquired				$ 10,000
Amortization period				10 years
Approximate value of acquisition				$ 19,000
Approximate additions to finite-lived intangible assets				$ 8,000