COMMITMENTS AND CONTINGENCIES - Schedule of minimum contractual obligations (Details 2) - USD ($) $ in Thousands		1 Months Ended		12 Months Ended
		Apr. 30, 2014	May. 31, 2012	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Railcar Lease
2016	[1]			$ 59,161
2017	[1]			55,500
2018	[1]			62,448
2019	[1]			66,618
2020	[1]			57,908
Thereafter	[1]			245,376
Total	[1]			547,011
Other Operating Leases
2016				1,607
2017				914
2018				574
2019				320
2020				269
Thereafter				2,774
Total				6,458
Royalty Commitments
2016				230
2017				230
2018				230
2019				230
2020				230
Thereafter				1,710
Total				2,860
Purchase Commitments
2016	[2]			27,556
2017	[2]			23,376
2018	[2]			24,517
2019	[2]			22,527
2020	[2]			21,322
Thereafter	[2]			48,805
Total	[2]			168,103
Less amount representing interest	[2]			(1,304)
Total less interest	[2]			166,799
Purchase Commitments and Railway Shipping Commitments
Term of railway shipping agreement			10 years
Operating Leases
Operating lease expense				$ 35,600	$ 21,500	$ 6,000
Capital Lease Obligations
Term of capital lease		5 years

[1] Includes minimum amounts payable under various operating leases as well estimated costs necessary to transport leased railcars from the manufacturer to our site for initial placement in service for those railcars to be delivered in the future.

[2] Includes various obligations for services as well as estimated payments for business acquisition obligation, inclusive of expected contingent consideration, based on forecasted volumes.