WORKERS' COMPENSATION AND PNEUMOCONIOSIS - Workers' Compensation Liability (Details) - USD ($) $ in Thousands						3 Months Ended		6 Months Ended
		Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reconciliation of the changes in workers' compensation liability
Beginning balance						$ 55,564	$ 58,198	$ 54,558	$ 57,557
Accruals increase						2,187	3,500	5,424	6,167
Payments						(3,265)	(2,100)	(5,988)	(4,614)
Interest accretion						492	489	984	977
Valuation loss (gain)	[1]					1,425	(4,416)	1,425	(4,416)
Ending balance		$ 56,403	$ 54,558	$ 55,671	$ 57,557	$ 56,403	$ 55,671	$ 56,403	$ 55,671
Workers' compensation discount rate		2.89%	3.63%	3.71%	3.41%

[1] The ARLP Partnership′s liability for the estimated present value of current workers′ compensation benefits is based on its actuarial estimates. The ARLP Partnership′s actuarial calculations are based on a blend of actuarial projection methods and numerous assumptions including claim development patterns, mortality, medical costs and interest rates. The ARLP Partnership conducted a mid-year review of its actuarial assumptions which resulted in a valuation loss in 2016 primarily attributable to a decrease in the discount rate used to calculate the estimated present value of future obligations from 3.63% at December 31, 2015 to 2.89% at June 30, 2016, partially offset by favorable changes in claims development. The ARLP Partnership′s mid-year 2015 actuarial review resulted in a valuation gain primarily attributable to favorable changes in claims development and an increase in the discount rate from 3.41% at December 31, 2014 to 3.71% at June 30, 2015.