COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure
Total rental expense	$ 34.7	$ 29.9	$ 32.8
Rights-of-way payments	7.9	7.4	7.1
Environmental Remediation
Commitments and Contingencies Disclosure
Operating expenses, net of recoveries	13.7	7.4	$ 8.2
Insurance settlements receivable	$ 4.2	$ 5.3