INCOME TAXES - UNRECOGNIZED TAX BENEFITS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the beginning and ending amount of gross unrecognized tax benefits
Balance at beginning of the period	$ 20.4	$ 22.1	$ 6.7
Changes in tax positions of prior years, net	1.1		1.5
Changes in tax positions of prior years, net		(1.1)
Additions from unrecognized tax benefits acquired			14.4
Reductions for lapse of statute of limitations	(0.1)	(0.6)	(0.5)
Revaluation of unrecognized tax benefits due to the Tax Act	(5.5)
Balance at the end	15.9	20.4	22.1
Unrecognized tax benefits that, if recognized, would impact the effective rate	8.2
Interest accrued related to unrecognized tax benefits	0.5	0.4
Alternative minimum tax (AMT) receivable	$ 50.2
Stock options
Net tax benefits from share-based transactions		$ 2.2	$ 2.6