CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
Major Customers
Total revenues	$ 527,291	$ 551,966	$ 439,041	$ 412,725	$ 542,050	$ 566,342	$ 604,619	$ 560,300	$ 1,931,023	$ 2,273,311	[1]	$ 2,300,324	[1]
Trade receivables	152,032				122,875				152,032	122,875
Revenues | Customer Concentration Risk | Customer A
Major Customers
Total revenues									253,465	343,483		301,191
Revenues | Customer Concentration Risk | Customer B
Major Customers
Total revenues									241,255	305,048		276,094
Revenues | Customer Concentration Risk | Customer C
Major Customers
Total revenues									265,642	312,150		$ 317,745
Trade accounts receivable | Customer Concentration Risk | Customers A, B, and C
Major Customers
Trade receivables	$ 42,500				$ 48,400				$ 42,500	$ 48,400

[1] Revenues included in the 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 and brokerage coal sales.