COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Commitments
Outstanding letters of credit	$ 13.6		$ 13.6		$ 13.8
Amount of outstanding surety bonds	92.3		92.3		$ 88.5
Rent expense	2.3	$ 2.1	5.0	$ 4.2
Guarantee Obligations | Downtown Columbia
Commitments
Loss contingency guaranteed amount limit	$ 1.0		$ 1.0