DISTRIBUTIONS OF AVAILABLE CASH - Quarterly Distributions (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended
	Feb. 20, 2018	Jan. 26, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
DISTRIBUTIONS OF AVAILABLE CASH
Quarterly distribution paid (in dollars per share)	$ 0.7425		$ 0.7350	$ 0.7300	$ 0.5500	$ 0.5500	$ 0.5500	$ 0.5500	$ 0.5500	$ 0.9600	$ 0.9600	$ 0.9600	$ 0.9375	$ 0.9150
Distributions declared (in dollars per unit)		$ 0.7425
Approximate distribution to be paid (in dollars)		$ 45.1