SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Financial Instruments Where Carrying Value and Fair Value Differ (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term obligations	$ 90.7	$ 95.7
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term obligations, fair value	$ 91.8