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Goodwill and Intangibles - Narrative (Details) - USD ($) |  | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | --- | ---
May 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Goodwill [Line Items] |  |  |  |  |  |
Goodwill |  | $ 445,600,000 | $ 444,300,000 | $ 445,600,000 | $ 444,700,000 | $ 212,800,000
Addition to provisional goodwill from acquisition |  | 0 | 231,500,000 |  |  |
Measurement period adjustment to previously recorded goodwill |  | $ 900,000 | $ 0 |  |  |
Impairment of goodwill |  |  |  | $ 0 |  |
Core Deposits |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Weighted average useful lives of related deposits |  |  |  | 10 years |  |
Core Deposits | Bank of the Cascades |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Weighted average useful lives of related deposits | 10 years |  |  |  |  |

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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267 + Details
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