SUBSEQUENT EVENTS - Distributions (Details) - Subsequent event $ / shares in Units, $ in Millions	Oct. 27, 2017 USD ($) $ / shares
Subsequent Event
Distributions declared (in dollars per unit) | $ / shares	$ 0.735
Approximate distribution to be paid (in dollars)	$ 44.0
MGP
Subsequent Event
Approximate distribution to be paid	$ 0.7
ARLP
Subsequent Event
Distributions declared (in dollars per unit) | $ / shares	$ 0.505
Approximate distribution to be paid	$ 66.7