NONCONTROLLING INTERESTS - Partners' Capital (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Dec. 31, 1999
Noncontrolling Interest
Noncontrolling interests	$ 450,475	$ 441,748
ARLP
Noncontrolling Interest
Units owned by parent	31,088,338
Accumulated Other Comprehensive Loss Attributable To Noncontrolling Interests
Noncontrolling Interest
Noncontrolling interests	$ (19,571)	(19,682)
SGP
Noncontrolling Interest
Noncontrolling interests	$ (303,832)	(303,822)	$ (303,900)
SGP | ARLP
Noncontrolling Interest
Ownership percentage by noncontrolling owners	0.01%
SGP | Intermediate Partnership
Noncontrolling Interest
Ownership percentage by noncontrolling owners	0.01%
Non-Affiliates (ARLP's non-affiliate limited partners)
Noncontrolling Interest
Noncontrolling interests	$ 769,997	762,667
Affiliate (Cavalier Minerals)
Noncontrolling Interest
Noncontrolling interests	$ 3,881	$ 2,585