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Fair Value Measurements - Narrative (Details) - USD ($) | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Related allowance | $ 10,800,000 | $ 14,000,000 | $ 11,600,000
Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Impaired loans | 22,200,000 | (25,800,000) |
Carrying value of assets to be disposed of | 800,000 | 2,400,000 |
Write down of assets to be disposed of | 0 | 1,100,000 |
Fair value of assets to be disposed of | 800,000 | 1,300,000 |
Fair Value Measured on a Non-recurring Basis | Significant Unobservable Inputs (Level 3) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Impaired loans | 32,600,000 | 39,300,000 |
Related allowance | 10,700,000 | 14,000,000 |
Partial loan charge-off | 11,400,000 | 11,900,000 |
Carrying Amount | Fair Value Measured on a Non-recurring Basis | Significant Unobservable Inputs (Level 3) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Impaired loans | 54,700,000 | 65,200,000 |
Estimated Fair Value | Fair Value Measured on a Non-recurring Basis |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Impaired loans | 32,600,000 | 39,300,000 |
Estimated Fair Value | Fair Value Measured on a Non-recurring Basis | Significant Unobservable Inputs (Level 3) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Impaired loans | $ 32,600,000 | $ 39,300,000 |

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- Definition Amount of allowance for credit losses related to recorded investment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524 + Details
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