Quarterly report pursuant to Section 13 or 15(d)

Investments in Affiliated Companies - Narratives (Details)

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Investments in Affiliated Companies - Narratives (Details) - Business Combination - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Business Acquisition [Line Items]          
Purchase accounting fair value adjustments     $ 266,358   $ 273,300
Equity method investment, amortization expense $ 1,660 $ 12,291 $ 6,942 $ 24,606