BASIS OF PRESENTATION, CONSOLIDATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017 USD ($) aircraft	Sep. 30, 2016 USD ($) aircraft	Sep. 30, 2017 USD ($) aircraft	Sep. 30, 2016 USD ($) aircraft
Property, Plant and Equipment [Line Items]
Number of aircraft delivered | aircraft	2	6	5	6
Capital expenditures	$ 11,764	$ 80,803	$ 24,317	$ 101,866
Progress payments for aircraft	$ 1,000	$ 63,700	$ 2,300	$ 66,800
Medium
Property, Plant and Equipment [Line Items]
Number of aircraft delivered | aircraft	2	5	5	5
SAR aircraft
Property, Plant and Equipment [Line Items]
Number of aircraft delivered | aircraft	0	1	0	1
Aircraft and equipment
Property, Plant and Equipment [Line Items]
Capital expenditures	$ 5,679	$ 78,087	$ 16,489	$ 95,574
Land and buildings
Property, Plant and Equipment [Line Items]
Capital expenditures	$ 6,085	$ 2,716	$ 7,828	$ 6,292