INVENTORIES (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Inventory Disclosure [Abstract]
Coal stockpiles	$ 863	$ 989
Coal fuel inventories	4,068	3,048
Materials and supplies	35,505	34,954
Reserve for obsolete inventory	(1,102)	(1,257)
Total	$ 39,334	$ 37,734