VARIABLE INTEREST ENTITIES AND EQUITY INVESTMENTS AND ADVANCES Schedule of Equity Method Investment, Financial Information, Balance Sheets (Details) - Dart Helicopter Services LLC $ in Thousands	Dec. 31, 2018 USD ($)
Schedule of Equity Method Investments [Line Items]
Current assets	$ 31,332
Non-current assets	30,613
Current liabilities	7,007
Non-current liabilities	$ 5,558