COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Commitments
Outstanding letters of credit	$ 13.8		$ 13.8
Amount of outstanding surety bonds	92.9		$ 88.5
Rent expense	2.6	$ 2.1
Guarantee Obligations | Downtown Columbia
Commitments
Loss contingency guaranteed amount limit	$ 1.0
Period for guarantee after bond issue	36 months