Annual report pursuant to Section 13 and 15(d)

VARIABLE INTEREST ENTITIES AND EQUITY INVESTMENTS AND ADVANCES Dart Narrative (Details)

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VARIABLE INTEREST ENTITIES AND EQUITY INVESTMENTS AND ADVANCES Dart Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Apr. 01, 2019
Mar. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2009
Jul. 31, 2011
Feb. 28, 2011
Dec. 31, 2008
Schedule of Equity Method Investments [Line Items]                  
Cash proceeds $ 38,000                
Gain (loss) on disposition of business $ 10,900                
Dividends received from equity investees     $ 0 $ 1,000 $ 0        
Corporate Joint Venture                  
Schedule of Equity Method Investments [Line Items]                  
Purchases from related party   $ 600   2,000 2,000        
Dart Helicopter Services LLC                  
Schedule of Equity Method Investments [Line Items]                  
Additional investment               $ 5,000  
Dart Helicopter Services LLC | Equity Method Investee                  
Schedule of Equity Method Investments [Line Items]                  
Notes receivable to related party           $ 300      
Notes receivable interest rate           5.00%      
Dart Helicopter Services LLC | Era DHS LLC                  
Schedule of Equity Method Investments [Line Items]                  
Ownership                 49.00%
Dart Holding Company Ltd.                  
Schedule of Equity Method Investments [Line Items]                  
Expenses from transactions with related party       27,100 $ 2,000        
Dart Holding Company Ltd. | Equity Method Investee                  
Schedule of Equity Method Investments [Line Items]                  
Notes receivable to related party       $ 2,300     $ 5,100