SUBSEQUENT EVENTS - Distributions (Details) - Subsequent event $ / shares in Units, $ in Millions	Jul. 28, 2017 USD ($) $ / shares
Subsequent Event
Distributions declared (in dollars per unit) | $ / shares	$ 0.73
Approximate distribution to be paid (in dollars)	$ 43.7
MGP
Subsequent Event
Approximate distribution to be paid	$ 0.7
ARLP
Subsequent Event
Distributions declared (in dollars per unit) | $ / shares	$ 0.50
Approximate distribution to be paid	$ 66.0