BASIS OF PRESENTATION, CONSOLIDATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment (Details) $ in Thousands	3 Months Ended
	Jun. 30, 2018 USD ($) aircraft	Jun. 30, 2017 USD ($) aircraft
Property, Plant and Equipment [Line Items]
Number of aircraft delivered | aircraft	0	3
Capital expenditures	$ 8,895	$ 12,553
Progress payments for aircraft	$ 0	$ 1,300
Medium
Property, Plant and Equipment [Line Items]
Number of aircraft delivered | aircraft	0	3
Aircraft and equipment
Property, Plant and Equipment [Line Items]
Capital expenditures	$ 8,337	$ 10,810
Land and buildings
Property, Plant and Equipment [Line Items]
Capital expenditures	$ 558	$ 1,743