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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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 increase (decrease) from adjustments after acquisition date under purchase accounting 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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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Goodwill and Intangibles - Narrative (Details) $ in Millions		3 Months Ended		12 Months Ended
	Aug. 16, 2018 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)
Goodwill [Line Items]
Goodwill		$ 546.3	$ 445.6	$ 546.7	$ 444.7
Measurement period adjustment to previously recorded goodwill		$ (0.4)	$ 0.9
Inland Northwest Bank
Goodwill [Line Items]
Goodwill	$ 100.7
Number of Operating Segments \| segment				1
Core Deposits
Goodwill [Line Items]
Weighted average useful lives of related deposits		10 years
Core Deposits \| Inland Northwest Bank
Goodwill [Line Items]
Weighted average useful lives of related deposits	10 years