COMMITMENTS AND CONTINGENCIES (Details) $ in Thousands		3 Months Ended				6 Months Ended
	Apr. 29, 2016 aircraft People	Dec. 31, 2016 aircraft	Sep. 30, 2016 USD ($) aircraft Facility	Jun. 30, 2016 aircraft	Sep. 30, 2015 USD ($) aircraft	Sep. 30, 2016 USD ($) aircraft Facility	Sep. 30, 2015 USD ($) aircraft
Commitments And Contingencies [Abstract]
Purchase commitments | $			$ 297,800			$ 297,800
Number of fatalities | People	13
Number of signed client contracts			7			7
Aircraft Delivered			(6)		(1)	(6)	(3)
Rent expense | $			$ 51,900		$ 54,400	$ 103,200	$ 108,300
Operating leases, term of contract						180 months
Operating leases, renewal term						240 months
Number of leased aircraft			91			91
Site contingency, number of locations | Facility			3			3
Maximum
Commitments And Contingencies [Abstract]
Loss Contingency, Estimate of Possible Loss | $			$ 7,000			$ 7,000
Minimum
Commitments And Contingencies [Abstract]
Loss Contingency, Estimate of Possible Loss | $			5,000			5,000
Passenger
Commitments And Contingencies [Abstract]
Number of fatalities | People	11
Crew
Commitments And Contingencies [Abstract]
Number of fatalities | People	2
Voluntary Separation Program
Commitments And Contingencies [Abstract]
Severance costs | $			590		886	1,468	7,274
Voluntary Separation Program | Direct cost
Commitments And Contingencies [Abstract]
Severance costs | $			590		886	1,445	6,677
Voluntary Separation Program | General administrative expense
Commitments And Contingencies [Abstract]
Severance costs | $			0		0	23	597
Involuntary Separation Program
Commitments And Contingencies [Abstract]
Severance costs | $			8,963		4,814	13,491	6,417
Involuntary Separation Program | Direct cost
Commitments And Contingencies [Abstract]
Severance costs | $			4,398		2,045	4,896	2,561
Involuntary Separation Program | General administrative expense
Commitments And Contingencies [Abstract]
Severance costs | $			$ 4,565		$ 2,769	$ 8,595	$ 3,856
Unionized Employees Concentration Risk | Workforce Subject to Collective Bargaining Arrangements
Commitments And Contingencies [Abstract]
Concentration risk, percentage						57.00%
Collective bargaining agreements, maximum annual escalation per employee, percent						4.00%
Unionized Employees Concentration Risk | Workforce Subject to Collective Bargaining Arrangements Expiring within One Year
Commitments And Contingencies [Abstract]
Concentration risk, percentage						76.00%
Six months ending March 31, 2017 to fiscal year 2018
Commitments And Contingencies [Abstract]
Number of leased aircraft			19			19
Fiscal year 2019 to fiscal year 2021
Commitments And Contingencies [Abstract]
Number of leased aircraft			56			56
Fiscal year 2022 to fiscal year 2025
Commitments And Contingencies [Abstract]
Number of leased aircraft			16			16
Medium aircraft
Commitments And Contingencies [Abstract]
Aircraft Delivered			(5)		0	(5)	(1)
U.K. SAR
Commitments And Contingencies [Abstract]
Aircraft Delivered			(1)		(1)	(1)	(2)
H225 Super Puma
Commitments And Contingencies [Abstract]
Number of aircraft operated	27
Number of aircraft owned	16
Number of leased aircraft	11
H225 Super Puma | Norway
Commitments And Contingencies [Abstract]
Number of aircraft operated	5
H225 Super Puma | Norway | Commercial purpose aircraft | Subsequent event
Commitments And Contingencies [Abstract]
Number of aircraft suspended		1
H225 Super Puma | Norway | Search And Rescue purpose aircraft | Subsequent event
Commitments And Contingencies [Abstract]
Number of aircraft suspended		4
H225 Super Puma | United Kingdom
Commitments And Contingencies [Abstract]
Number of aircraft operated	13
H225 Super Puma | United Kingdom | Commercial purpose aircraft | Subsequent event
Commitments And Contingencies [Abstract]
Number of aircraft suspended		13
H225 Super Puma | Australia
Commitments And Contingencies [Abstract]
Number of aircraft operated	9
H225 Super Puma | Australia | Commercial purpose aircraft | Subsequent event
Commitments And Contingencies [Abstract]
Number of aircraft suspended		6
H225 Super Puma | Australia | Search And Rescue purpose aircraft | Subsequent event
Commitments And Contingencies [Abstract]
Number of aircraft suspended		3
Aircraft
Commitments And Contingencies [Abstract]
Rent expense | $			$ 46,100		$ 47,300	$ 90,800	$ 93,900
Commitments
Commitments And Contingencies [Abstract]
Beginning of quarter		35	36	36		36
Aircraft Delivered			(6)	0
Aircraft ordered			5	0
Expired options			0	0
End of quarter			35	36		35
Options
Commitments And Contingencies [Abstract]
Beginning of quarter		6	10	14		14
Aircraft Delivered			0	0
Aircraft ordered			0	0
Expired options			(4)	(4)
End of quarter			6	10		6
Aircraft
Commitments And Contingencies [Abstract]
Number of aircraft purchase commitments, due remainder of fiscal year			3			3
Number of aircraft purchase commitments, due in two years			9			9
Number of aircraft purchase commitments, due in three years			5			5
Number of aircraft purchase commitments, due in four years			4			4
Number of aircraft purchase commitments, due in five years and after			14			14
Number of aircraft purchase commitments			35			35
Purchase commitments, due remainder of year | $			$ 9,231			$ 9,231
Purchase commitments, Due within Two Years | $			60,471			60,471
Purchase commitments, Due within Three Years | $			92,734			92,734
Purchase commitments, Due within Four Years | $			72,133			72,133
Purchase commitments, Due within Five Years And After | $			194,625			194,625
Purchase commitments | $			$ 429,194			$ 429,194
Number of aircraft purchase options, due remainder of fiscal year			0			0
Number of aircraft purchase options, due in two years			4			4
Number of aircraft purchase options, due in three years			2			2
Number of aircraft purchase options, due in four years			0			0
Number of aircraft purchase options, due in five years and after			0			0
Number of aircraft purchase options			6			6
Aircraft purchase options, due remainder of year | $			$ 5,429			$ 5,429
Aircraft purchase options, due in two years | $			64,806			64,806
Aircraft purchase options, due in three years | $			30,410			30,410
Aircraft purchase options, due in four years | $			0			0
Aircraft purchase options, due in five years and after | $			0			0
Aircraft purchase options | $			$ 100,645			$ 100,645
Aircraft | Medium aircraft
Commitments And Contingencies [Abstract]
Number of aircraft purchase commitments, due remainder of fiscal year			0			0
Number of aircraft purchase commitments, due in two years			5			5
Number of aircraft purchase commitments, due in three years			0			0
Number of aircraft purchase commitments, due in four years			0			0
Number of aircraft purchase commitments, due in five years and after			0			0
Number of aircraft purchase commitments			5			5
Number of aircraft purchase options, due remainder of fiscal year			0			0
Number of aircraft purchase options, due in two years			2			2
Number of aircraft purchase options, due in three years			0			0
Number of aircraft purchase options, due in four years			0			0
Number of aircraft purchase options, due in five years and after			0			0
Number of aircraft purchase options			2			2
Aircraft | Large aircraft
Commitments And Contingencies [Abstract]
Number of aircraft purchase commitments, due remainder of fiscal year			0			0
Number of aircraft purchase commitments, due in two years			0			0
Number of aircraft purchase commitments, due in three years			5			5
Number of aircraft purchase commitments, due in four years			4			4
Number of aircraft purchase commitments, due in five years and after			14			14
Number of aircraft purchase commitments			23			23
Number of aircraft purchase options, due remainder of fiscal year			0			0
Number of aircraft purchase options, due in two years			2			2
Number of aircraft purchase options, due in three years			2			2
Number of aircraft purchase options, due in four years			0			0
Number of aircraft purchase options, due in five years and after			0			0
Number of aircraft purchase options			4			4
Aircraft | Medium and Large Aircrafts
Commitments And Contingencies [Abstract]
Purchase commitments, due remainder of year | $			$ 4,598			$ 4,598
Purchase commitments, Due within Two Years | $			2,263			2,263
Purchase commitments, Due within Three Years | $			92,734			92,734
Purchase commitments, Due within Four Years | $			72,133			72,133
Purchase commitments, Due within Five Years And After | $			194,625			194,625
Purchase commitments | $			$ 366,353			$ 366,353
Aircraft | U.K. SAR
Commitments And Contingencies [Abstract]
Number of aircraft purchase commitments, due remainder of fiscal year			3			3
Number of aircraft purchase commitments, due in two years			4			4
Number of aircraft purchase commitments, due in three years			0			0
Number of aircraft purchase commitments, due in four years			0			0
Number of aircraft purchase commitments, due in five years and after			0			0
Number of aircraft purchase commitments			7			7
Purchase commitments, due remainder of year | $			$ 4,633			$ 4,633
Purchase commitments, Due within Two Years | $			58,208			58,208
Purchase commitments, Due within Three Years | $			0			0
Purchase commitments, Due within Four Years | $			0			0
Purchase commitments, Due within Five Years And After | $			0			0
Purchase commitments | $			$ 62,841			$ 62,841
Cancellable commitments
Commitments And Contingencies [Abstract]
Number of aircraft purchase commitments			5			5
Purchase commitments | $			$ 83,700			$ 83,700
Deposit | $			$ 4,500			$ 4,500