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, 2016
Dec. 31, 2015
Dart Helicopter Services LLC    
Schedule of Equity Method Investments [Line Items]    
Current assets $ 28,442 $ 22,567
Non-current assets 29,475 30,716
Current liabilities 6,737 4,225
Non-current liabilities 8,315 8,850
Other Investments    
Schedule of Equity Method Investments [Line Items]    
Current assets 535 703
Non-current assets 4,641 5,159
Current liabilities 653 597
Non-current liabilities $ 3,652 $ 3,984