UNITHOLDERS' EQUITY AND PARTNERSHIP DISTRIBUTIONS (Details) - $ / shares	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Common units
Units issued (in units)								23,520,219	18,056,487
Units outstanding (in units)	23,520,219		18,056,487				18,056,487	23,520,219	18,056,487
Capital rollforward
Unitholders' capital, beginning balance (in units)			18,056,487				18,056,487
Unitholders' capital, ending balance (in units)	23,520,219						23,520,219
Cash distributions declared and paid (in dollars per unit)	$ 0.42	$ 0.39	$ 0.37	$ 0.45	$ 0.43	$ 0.42
Common Units
Common units
Units issued (in units)								23,520,219
Units outstanding (in units)	23,520,219		18,056,487				18,056,487	23,520,219	18,056,487
Capital rollforward
Unitholders' capital, beginning balance (in units)			18,056,487				18,056,487
Conversion of Class B Units (in units)							5,465,000
Restricted units used for tax withholding (in units)							(1,268)
Unitholders' capital, ending balance (in units)	23,520,219						23,520,219
Class B
Common units
Units outstanding (in units)	23,388,258		19,453,258				19,453,258	23,388,258	19,453,258
Capital rollforward
Unitholders' capital, beginning balance (in units)			19,453,258				19,453,258
Units issued to acquisition (in units)							9,400,000
Conversion of Class B Units (in units)							(5,465,000)
Unitholders' capital, ending balance (in units)	23,388,258						23,388,258
Cash distributions (as a percent)							2.00%