Annual report pursuant to Section 13 and 15(d)

Investments in Affiliated Companies - Summarized Balance Sheet (Details)

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Investments in Affiliated Companies - Summarized Balance Sheet (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]    
Current assets $ 215,416 $ 213,815
Noncurrent assets 248,288 235,440
Current liabilities 40,536 37,018
Noncurrent liabilities $ 56 $ 1,417