COMPENSATION PLANS - LTIP Grants Activity (Details) - ARLP LTIP - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of non-vested grants (in units)
Balance at the beginning of the period (in units)	939,793	843,340	695,532
Granted (in units)	960,992	303,165	356,154
Vested (in units)	(284,272)	(202,778)	(202,742)
Forfeited (in units)	(11,765)	(3,934)	(5,604)
Balance at the end of the period (in units)	1,604,748	939,793	843,340
Weighted average grant date fair value per unit
Balance at the beginning of the period (in dollars per unit)	$ 36.80	$ 37.16	$ 34.23
Granted (in dollars per unit)	12.38	37.18	40.72
Vested (in dollars per unit)	31.51	38.85	33.42
Forfeited (in dollars per unit)	26.39	36.49	35.88
Balance at the end of the period (in dollars per unit)	$ 23.19	$ 36.80	$ 37.16
Intrinisic value (in dollars)
Intrinsic value of outstanding grants (in dollars)	$ 36,027	$ 12,678	$ 36,306	$ 26,778
Other information
Common units issued upon vesting	176,319	128,150	128,610