COMMITMENTS AND CONTINGENCIES - Purchase Commitment Narrative (Details) - Aircraft	6 Months Ended
Sep. 30, 2018 aircraft
Schedule Of Aircraft Purchase Contracts [Line Items]
Purchase commitment period	7 years
Number of minimum quantity required in a purchase obligation	27
Number of minimum quantity required in purchase options	4

The minimum number of units that must be purchased, in connection with an unconditional purchase obligation that has not been recognized for financial reporting purposes.

No definition available.

Name:	us-gaap_UnrecordedUnconditionalPurchaseObligationMinimumQuantityRequired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant