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Basis of Presentation and Significant Accounting Policies Supplemental Cash Flow Information (Tables) | 12 Months Ended
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Dec. 31, 2017
Schedule of Cash Flow Supplemental Information [Line Items] |
Schedule of Supplemental Cash Flow Information [Table Text Block] | Supplemental Disclosure of Cash Flow Information:
(Dollars in thousands) Year Ended December 31, |  | 2017 |  | 2016 |  | 2015
Cash paid during the period for: |  |  |  |  |  |
Income taxes |  | $ | 40,334 |  |  | $ | 21,437 |  |  | $ | 16,969 |
Interest on long-term debt and investment agreements |  | 39,112 |  |  | 4,537 |  |  | 1,847 |
Non-cash financing activities: |  |  |  |  |  |
Decrease in long-term debt as a result of an exchange for investment securities |  | 55,426 |  |  | — |  |  | — |

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- Definition Schedule of Supplemental Cash Flow Information [Table Text Block] + References No definition available. + Details
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