INCOME TAXES - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) state	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Income Tax Disclosure [Line Items]
Recognized share-based compensation tax benefit		$ 2.9
Decrease in deferred income tax expense from remeasurement of deferred taxes due to change in tax rate (Tax Cuts and Jobs Act)	$ 21.4
Income tax receivable	3.4	3.4	$ 1.3
Reduction in uncertain tax positions from change in enacted tax rate		1.1	0.0
Uncertain tax benefits accrued	2.7	2.7	4.1	$ 4.7
Valuation allowance	0.7	0.7	0.4
Net change in total valuation allowance		0.3	0.1
Interest and penalties recognized related to uncertain income tax positions		(0.1)	(0.1)
Interest and penalties accrued related to uncertain income tax positions	0.1	$ 0.1	0.1
Number of individual states subject to income taxes | state		50
Minimum [Member]
Income Tax Disclosure [Line Items]
Tax years open to examination		2001
Maximum [Member]
Income Tax Disclosure [Line Items]
Tax years open to examination		2017
Other Long Term Obligations [Member]
Income Tax Disclosure [Line Items]
Uncertain tax benefits accrued	2.7	$ 2.7
Net Operating Loss [Member]
Income Tax Disclosure [Line Items]
Uncertain tax benefits accrued	2.1	2.1	3.1
Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Uncertain tax benefits accrued	0.7	0.7	$ 0.7
Alternative Minimum Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credits		$ 2.3
Alternative Minimum Tax Credit [Member] | Minimum [Member]
Income Tax Disclosure [Line Items]
Refund tax year		2018
Alternative Minimum Tax Credit [Member] | Maximum [Member]
Income Tax Disclosure [Line Items]
Refund tax year		2020
Research And Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credits		$ 1.9
Employment Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credits		0.4
State Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credits		3.8
Federal [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	52.6	52.6
State and Local Jurisdiction [Member] | Net Operating Loss [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 223.0	$ 223.0