STOCKHOLDERS' EQUITY - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in accumulated other comprehensive income (loss), net of tax
Beginning Balance	$ 386.5	$ 358.7	$ 309.4
Other comprehensive income (loss) before reclassifications	(23.1)	(25.3)	(2.8)
Amounts reclassified from AOCL	22.1	5.9	1.4
Net current period other comprehensive loss before income tax	(1.0)	(19.4)	(1.4)
Income tax benefit (expense)	0.0	(0.5)	1.0
Other comprehensive loss (income)	(1.0)	(19.9)	(0.4)
Ending Balance	427.6	386.5	358.7
Unrealized gains (losses) on Interest Rate Swaps
Changes in accumulated other comprehensive income (loss), net of tax
Beginning Balance	(1.2)	0.0	0.0
Other comprehensive income (loss) before reclassifications	(6.0)	(1.6)	0.0
Amounts reclassified from AOCL	1.1	0.0	0.0
Net current period other comprehensive loss before income tax	(4.9)	(1.6)	0.0
Income tax benefit (expense)	1.3	0.4	0.0
Other comprehensive loss (income)	(3.6)	(1.2)	0.0
Ending Balance	(4.8)	(1.2)	0.0
Foreign Currency Translation Adjustment
Changes in accumulated other comprehensive income (loss), net of tax
Beginning Balance	(18.8)	(5.6)	(14.0)
Other comprehensive income (loss) before reclassifications	3.2	(13.2)	8.4
Amounts reclassified from AOCL	0.0	0.0	0.0
Net current period other comprehensive loss before income tax	3.2	(13.2)	8.4
Income tax benefit (expense)	0.0	0.0	0.0
Other comprehensive loss (income)	3.2	(13.2)	8.4
Ending Balance	(15.6)	(18.8)	(5.6)
Foreign Currency Translation Adjustment on Long-term Intercompany Notes
Changes in accumulated other comprehensive income (loss), net of tax
Beginning Balance	(8.1)	0.0	0.0
Other comprehensive income (loss) before reclassifications	(4.9)	(8.1)	0.0
Amounts reclassified from AOCL	0.0	0.0	0.0
Net current period other comprehensive loss before income tax	(4.9)	(8.1)	0.0
Income tax benefit (expense)	0.0	0.0	0.0
Other comprehensive loss (income)	(4.9)	(8.1)	0.0
Ending Balance	(13.0)	(8.1)	0.0
Pension and Other Post-Employment Liability Adjustment
Changes in accumulated other comprehensive income (loss), net of tax
Beginning Balance	(40.3)	(38.2)	(29.4)
Other comprehensive income (loss) before reclassifications	(15.4)	(2.4)	(11.2)
Amounts reclassified from AOCL	21.0	5.9	1.4
Net current period other comprehensive loss before income tax	5.6	3.5	(9.8)
Income tax benefit (expense)	(1.3)	(0.9)	1.0
Other comprehensive loss (income)	4.3	2.6	(8.8)
ASU 2018-02		(4.7)
Ending Balance	(36.0)	(40.3)	(38.2)
Total
Changes in accumulated other comprehensive income (loss), net of tax
Beginning Balance	(68.4)	(43.8)	(43.4)
ASU 2018-02		(4.7)
Ending Balance	$ (69.4)	$ (68.4)	$ (43.8)