BASIS OF PRESENTATION, CONSOLIDATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018 USD ($) aircraft	Sep. 30, 2017 USD ($) aircraft	Sep. 30, 2018 USD ($) aircraft	Sep. 30, 2017 USD ($) aircraft
Property, Plant and Equipment [Line Items]
Number of aircraft delivered | aircraft	0	2	0	5
Capital expenditures	$ 8,407	$ 11,764	$ 17,302	$ 24,317
Progress payments for aircraft	$ 0	$ 1,000	$ 0	$ 2,300
Medium
Property, Plant and Equipment [Line Items]
Number of aircraft delivered | aircraft	0	2	0	5
Aircraft and equipment
Property, Plant and Equipment [Line Items]
Capital expenditures	$ 4,394	$ 5,679	$ 12,731	$ 16,489
Land and buildings
Property, Plant and Equipment [Line Items]
Capital expenditures	$ 4,013	$ 6,085	$ 4,571	$ 7,828