COMMITMENTS AND CONTINGENCIES - Schedule of Purchase Commitment and Commitment Expenditures (Details) - Aircraft $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2019 aircraft	Sep. 30, 2019 USD ($) aircraft	Sep. 30, 2019 USD ($) aircraft	Jul. 25, 2019 USD ($) aircraft	Mar. 31, 2019 aircraft
Number of Aircraft Unconditional Commitments
Purchase Commitment - Total Aircrafts		3	3
U.K. SAR
Number of Aircraft Unconditional Commitments
Six Months Ending March 31, 2020		2	2
2020		1	1
2021		0	0
2022		0	0
2023 and thereafter		0	0
Purchase Commitment - Total Aircrafts		3	3	4
Commitment Expenditures
Six Months Ending March 31, 2020 | $		$ 28,747	$ 28,747
2020 | $		14,374	14,374
2021 | $		0	0
2022 | $		0	0
2023 and thereafter | $		0	0
Purchase Commitments - Total | $		$ 43,121	$ 43,121
Postponement Of Commitments, Number of Aircraft				3
Capital expenditure deferral | $				$ 14,400
Number of leased aircraft					3
Number Of Aircraft Purchased		1
Large Aircraft [Member]
Commitment Expenditures
Bankruptcy Claims, Number of Claims on Material Contracts Rejected			22
Subsequent Event [Member] | Large Aircraft [Member]
Commitment Expenditures
Bankruptcy Claims, Number of Claims on Material Contracts Rejected	22