COMMITMENTS AND CONTINGENCIES - Environmental Contingencies, Other Purchase Obligations and Other Matters (Details)	3 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Mar. 10, 2019 USD ($)	Feb. 28, 2019 USD ($) shares	Jan. 08, 2019 USD ($)	Dec. 31, 2018 USD ($) Facility
Other Commitments [Line Items]
Number of former waste disposal facilities | Facility							3
High
Other Commitments [Line Items]
Estimate of possible loss							$ 3,000,000
Other Commitments
Other Commitments [Line Items]
Purchase obligations							$ 52,000,000
Subsequent Event [Member] | Sikorsky Lawsuit [Member]
Other Commitments [Line Items]
Deposits Assets						$ 11,700,000
Subsequent Event [Member] | Huntington Lawsuit [Member]
Other Commitments [Line Items]
Loss Contingency, Damages Sought, Value			$ 2,500,000
Counterclaim, Damages Sought, Value	$ 100,000
Subsequent Event [Member] | Pilot [Member]
Other Commitments [Line Items]
Number Of Fatality				1
Subsequent Event [Member] | Passenger [Member]
Other Commitments [Line Items]
Number Of Fatality				1
Chief Executive Officer [Member] | Subsequent Event [Member] | Special Termination Benefits [Member]
Other Commitments [Line Items]
Consulting Fee, To Be Paid Per Month					$ 30,000
Severance costs		$ 1,442,000
COBRA Coverage Period		18 months
COBRA Coverage Period, Extension		36 months
Outplacement Service, Period		12 months
Non-Compete Period, Original		1 year
Non-Compete Period, Amended		2 years
Chief Executive Officer [Member] | Subsequent Event [Member] | Special Termination Benefits [Member] | Restricted Stock Units (RSUs) [Member]
Other Commitments [Line Items]
Options To Purchase, Number of Shares | shares					23,927
Chief Executive Officer [Member] | Subsequent Event [Member] | Special Termination Benefits [Member] | Share-based Compensation Award, Tranche One [Member] | Employee Stock Option [Member]
Other Commitments [Line Items]
Options To Purchase, Number of Shares | shares					43,503
Chief Executive Officer [Member] | Subsequent Event [Member] | Special Termination Benefits [Member] | Share-based Compensation Award, Tranche Two [Member] | Employee Stock Option [Member]
Other Commitments [Line Items]
Options To Purchase, Number of Shares | shares					102,190
Chief Executive Officer [Member] | Subsequent Event [Member] | Special Termination Benefits [Member] | Share-based Compensation Award, Tranche Three [Member] | Employee Stock Option [Member]
Other Commitments [Line Items]
Options To Purchase, Number of Shares | shares					74,502