FAIR VALUE DISCLOSURES - Assets at Fair Value On A Non-recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventories	$ 117,706		$ 117,706		$ 129,614
Aircraft and equipment	2,491,291		2,491,291		2,511,131
Assets held for sale	24,176		24,176		$ 30,348
Impairment of inventories	(9,276)	$ 0	(9,276)	$ (1,192)
Impairment of property and equipment	(104,939)	0	(104,939)	0
Impairment of intangible assets	(3,005)	0	(3,005)	0
Impairment charges on aircraft held for sale	0	(8,183)	0	(9,747)
Loss on sale of assets and asset impairment charges	(117,220)	(8,183)	(117,220)	(10,939)
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventories	7,697	1,218	7,697	1,218
Aircraft and equipment	136,338		136,338
Other intangible assets	0		0
Assets held for sale		36,167		36,167
Total assets	144,035	37,385	144,035	37,385
Fair Value, Measurements, Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventories	0	0	0	0
Aircraft and equipment	0		0
Other intangible assets	0		0
Assets held for sale		0		0
Total assets	0	0	0	0
Fair Value, Measurements, Nonrecurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventories	0	1,218	0	1,218
Aircraft and equipment	0		0
Other intangible assets	0		0
Assets held for sale		36,167		36,167
Total assets	0	37,385	0	37,385
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventories	7,697	0	7,697	0
Aircraft and equipment	136,338		136,338
Other intangible assets	0		0
Assets held for sale		0		0
Total assets	$ 144,035	$ 0	$ 144,035	$ 0