INCOME TAXES (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2010
Consolidated provision for income taxes	$ 8,771,000	$ 12,121,000	$ 35,871,000	$ 42,131,000
Consolidated effective federal and state income tax rates (as a percent)	37.50%	36.70%	37.10%	37.00%
Net operating loss					22,000,000
Loss carry back period	2 years
Advanced coal investment tax credit								17,700,000
Maximum tax credit utilized						9,000,000	700,000
Expected to use | Low end of range
Maximum tax credit utilized	5,000,000		5,000,000
Expected to use | High end of range
Maximum tax credit utilized	$ 7,000,000		$ 7,000,000