SUBSEQUENT EVENTS (Details) - USD ($) $ / shares in Units, $ in Thousands			6 Months Ended
	Jul. 31, 2015	Jul. 28, 2015	Jun. 30, 2015
Subsequent Event
Cash paid at closing			$ 28,078
Subsequent event
Subsequent Event
Distributions declared (in dollars per unit)		$ 0.96
Approximate distribution to be paid		$ 57,500
Subsequent event | ARLP
Subsequent Event
Distributions declared (in dollars per unit)		$ 0.675
Approximate distribution to be paid, including incentive distributions		$ 87,500
Subsequent event | White Oak
Subsequent Event
Remaining equity interest acquired (as a percent)	60.00%
Cash paid at closing	$ 50,000
Percentage of equity interests in the acquiree owned as of the Acquisition Date	100.00%