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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 |  |  |  |

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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e961-128460 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267 + Details
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