COMMITMENTS AND CONTINGENCIES Aircraft Purchase Contracts (Details) $ in Thousands	Mar. 31, 2018 USD ($) aircraft
Other commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded unconditional purchase obligation | $	$ 48,300
Aircraft
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded unconditional purchase obligation minimum quantity required, due in one year	1
Unrecorded unconditional purchase obligation minimum quantity required, due in year two	4
Unrecorded unconditional purchase obligation minimum quantity required, due in year three	4
Unrecorded unconditional purchase obligation minimum quantity required, due in year four and thereafter	18
Unrecorded unconditional purchase obligation, minimum quantity required	27
Unrecorded unconditional purchase obligation, due within one year | $	$ 19,912
Unrecorded unconditional purchase obligation, due within two years | $	90,648
Unrecorded unconditional purchase obligation, due within three years | $	80,633
Unrecorded unconditional purchase obligation, due within four years and thereafter | $	292,204
Unrecorded unconditional purchase obligation | $	$ 483,397
Unrecorded conditional purchase obligation, maximum quantity required, due in one year	2
Unrecorded conditional purchase obligation, maximum quantity required, due in year two	2
Unrecorded conditional purchase obligation, maximum quantity required, due in year three	0
Unrecorded conditional purchase obligation, maximum quantity required, due in year four and thereafter	0
Unrecorded conditional purchase obligation, maximum quantity required	4
Unrecorded conditional purchase obligation balance on first anniversary | $	$ 44,181
Unrecorded conditional purchase obligation balance on second anniversary | $	31,536
Unrecorded conditional purchase obligation balance on third anniversary | $	0
Unrecorded Conditional Purchase Obligation Balance On Fourth Anniversary And After | $	0
Unrecorded conditional purchase obligation balance sheet amount | $	$ 75,717
Aircraft | Large Aircraft
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded unconditional purchase obligation minimum quantity required, due in one year	1
Unrecorded unconditional purchase obligation minimum quantity required, due in year two	0
Unrecorded unconditional purchase obligation minimum quantity required, due in year three	4
Unrecorded unconditional purchase obligation minimum quantity required, due in year four and thereafter	18
Unrecorded unconditional purchase obligation, minimum quantity required	23
Unrecorded conditional purchase obligation, maximum quantity required, due in one year	2
Unrecorded conditional purchase obligation, maximum quantity required, due in year two	2
Unrecorded conditional purchase obligation, maximum quantity required, due in year three	0
Unrecorded conditional purchase obligation, maximum quantity required, due in year four and thereafter	0
Unrecorded conditional purchase obligation, maximum quantity required	4
Aircraft | Medium And Large [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded unconditional purchase obligation, due within one year | $	$ 19,912
Unrecorded unconditional purchase obligation, due within two years | $	26,154
Unrecorded unconditional purchase obligation, due within three years | $	80,633
Unrecorded unconditional purchase obligation, due within four years and thereafter | $	292,204
Unrecorded unconditional purchase obligation | $	$ 418,903
Aircraft | U.K. SAR Configured Aircraft [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded unconditional purchase obligation minimum quantity required, due in one year	0
Unrecorded unconditional purchase obligation minimum quantity required, due in year two	4
Unrecorded unconditional purchase obligation minimum quantity required, due in year three	0
Unrecorded unconditional purchase obligation minimum quantity required, due in year four and thereafter	0
Unrecorded unconditional purchase obligation, minimum quantity required	4
Unrecorded unconditional purchase obligation, due within one year | $	$ 0
Unrecorded unconditional purchase obligation, due within two years | $	64,494
Unrecorded unconditional purchase obligation, due within three years | $	0
Unrecorded unconditional purchase obligation, due within four years and thereafter | $	0
Unrecorded unconditional purchase obligation | $	$ 64,494
Cancellable commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded unconditional purchase obligation, minimum quantity required	5
Unrecorded unconditional purchase obligation | $	$ 98,000
Deposits | $	$ 4,500