INCOME TAXES - Effective Income Tax Rate Variation from Stated Tax Rate (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Federal income tax statutory rate	35.00%
Income tax expense at statutory federal income tax rate	$ 18.5		$ 32.2	$ 27.9
State income taxes, net of federal income tax benefit	1.5		2.6	2.3
Other, net	(0.1)		(0.1)	0.1
Total income tax expense	$ 19.9	$ 22.9	$ 34.7	$ 30.3
Effective income tax rate (%)	37.60%		37.70%	38.00%