Investments in Affiliated Companies - Narratives (Details) - Business Combination - USD ($) $ in Thousands  | 
3 Months Ended | 6 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|---|
Jun. 30, 2018  | 
Jun. 30, 2017  | 
Jun. 30, 2018  | 
Jun. 30, 2017  | 
Dec. 31, 2017  | 
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| Business Acquisition | |||||
| Purchase accounting fair value adjustments | $ 261,384 | $ 264,700 | |||
| Charges related to purchase accounting fair value adjustments | $ 1,658 | $ 1,658 | $ 3,316 | $ 5,282 | |
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- Definition Equity Method Investments Charges Related to Purchase Accounting No definition available. 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Definition Amount of increase (decrease) in income that would have been recognized in previous periods if the adjustments to provisional amounts were recognized as of the acquisition date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Details 
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