Quarterly report pursuant to Section 13 or 15(d)

Equity Investments (Equity Investments Balance Sheet Disclosure) (Details)

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Equity Investments (Equity Investments Balance Sheet Disclosure) (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]    
Current assets $ 395,532 $ 415,032
Noncurrent assets 1,353,052 1,542,090
Current liabilities 368,377 261,086
Noncurrent liabilities $ 47,450 $ 148,839