LEASES - FUTURE MINIMUM LEASE PAYMENTS (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Total operating leases
Nine months ended December 31, 2019	$ 4.5
2020	7.1
2021	5.1
2022	5.1
2023	5.2
2024	5.1
Thereafter	33.0
Total minimum lease payments	65.1
Less: interest	(17.3)
Present value of minimum lease payments	47.8	$ 48.8
Less: short-term lease liabilities	(4.1)
Long-term lease liabilities	43.7
Power purchase commitment
Nine months ended December 31, 2019	6.2
2020	8.8
2021	9.4
2022	4.2
2023	0.0
2024	0.0
Thereafter	0.0
Total minimum lease payments	28.6
Less: interest	(6.5)
Present value of minimum lease payments	22.1
Less: short-term lease liabilities	(5.2)
Long-term lease liabilities	$ 16.9
Capital lease
Short-term liabilities under capital lease			$ 4.9
Long-term liabilities under capital lease			$ 18.4