ACCUMULATED OTHER COMPREHENSIVE LOSS - Reclassification out of Accumulated Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ (1,056.8)	$ (770.4)
Ending balance	(1,132.2)	(1,056.8)
Interest rate swap | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(0.1)	(0.7)
Reclassifications into earnings, net of tax		0.6
Ending balance		$ (0.1)
Other Comprehensive Income (Loss), Tax [Abstract]
Reclassifications into earnings - tax benefit	$ 0.2