SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016
Prior period corrections
Reclassification, decrease (increase) to expense	$ (0.8)
Termination and access fees
Prior period corrections
Reclassification, decrease (increase) to expense		$ 4.9
Engineering and operations expenses
Prior period corrections
Reclassification, decrease (increase) to expense		(7.5)
Equipment expense
Prior period corrections
Reclassification, decrease (increase) to expense		(0.6)
Selling and marketing expense.
Prior period corrections
Reclassification, decrease (increase) to expense		0.8
General and administrative expense
Prior period corrections
Reclassification, decrease (increase) to expense		$ 2.4