Annual report pursuant to Section 13 and 15(d)

VARIABLE INTEREST ENTITIES AND EQUITY INVESTMENTS AND ADVANCES Schedule of Equity Method Investment, Financial Information, Balance Sheets (Details)

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VARIABLE INTEREST ENTITIES AND EQUITY INVESTMENTS AND ADVANCES Schedule of Equity Method Investment, Financial Information, Balance Sheets (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Dart Helicopter Services LLC    
Schedule of Equity Method Investments [Line Items]    
Current assets $ 31,332 $ 29,336
Non-current assets 30,613 29,899
Current liabilities 7,007 6,671
Non-current liabilities 5,558 6,096
Other Investments    
Schedule of Equity Method Investments [Line Items]    
Current assets 0 257
Non-current assets 0 4,138
Current liabilities 0 654
Non-current liabilities $ 0 $ 3,298