WORKERS' COMPENSATION AND PNEUMOCONIOSIS (Details) - USD ($) $ in Thousands						3 Months Ended		6 Months Ended
		Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reconciliation of the changes in workers' compensation liability
Beginning balance						$ 58,198	$ 62,989	$ 57,557	$ 62,909
Accruals increase						3,500	5,281	6,167	7,464
Payments						(2,100)	(2,778)	(4,614)	(5,527)
Interest accretion						489	647	977	1,293
Valuation gain	[1]					(4,416)	(4,624)	(4,416)	(4,624)
Ending balance		$ 55,671	$ 57,557	$ 61,515	$ 62,909	$ 55,671	$ 61,515	$ 55,671	$ 61,515
Workers' compensation discount rate (as a percent)		3.71%	3.41%	3.67%	4.11%

[1] The liability for the estimated present value of current workers′ compensation benefits is based on the ARLP Partnership’s 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 gain in 2015 primarily attributable to favorable changes in claims development and an increase in the discount rate used to calculate the estimated present value of future obligations from 3.41% at December 31, 2014 to 3.71% at June 30, 2015. The ARLP Partnership’s mid-year 2014 actuarial review also resulted in a valuation gain primarily attributable to favorable changes in claims development, offset partially by a decrease in the utilized discount rate from 4.11% at December 31, 2013 to 3.67% at June 30, 2014.