CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Major Customers
Total revenues	$ 542,050	$ 566,342	$ 604,619	$ 560,300	$ 590,696	$ 569,230	$ 598,464	$ 541,934	$ 2,273,311	[1]	$ 2,300,324	[1]	$ 2,205,199	[1]
Trade receivables	122,875				184,187				122,875		184,187
Customers A and B
Major Customers
Trade receivables	$ 37,500				$ 43,500				37,500		43,500
Illinois Basin | Customer A
Major Customers
Total revenues									343,483		301,191		319,932
Illinois Basin | Customer B
Major Customers
Total revenues									$ 305,048		$ 276,094		$ 263,582

[1] Revenues included in Other and Corporate column are primarily attributable to the Matrix Group revenues, Mt. Vernon transloading revenues, administrative service revenues from affiliates, MAC revenues, Wildcat Insurance revenues, brokerage sales and Pontiki’s coal sales revenue (2013 only).