PARTNERS' CAPITAL - Partners' Capital and Schedule of Units (Details)	9 Months Ended
	Sep. 30, 2019 shares
Series A Preferred Units
Rollforwards of the number of partner units
Units, beginning balance (in shares)	300,000
Conversion of General Partner economic interests (in shares)	0
Net units issued under the SMLP LTIP (in shares)	0
Units, ending balance (in shares)	300,000
Common
Rollforwards of the number of partner units
Units, beginning balance (in shares)	73,390,853
Conversion of General Partner economic interests (in shares)	8,750,000
Net units issued under the SMLP LTIP (in shares)	607,492
Units, ending balance (in shares)	82,748,345
General Partner Units
Rollforwards of the number of partner units
Units, beginning balance (in shares)	1,490,999
Conversion of General Partner economic interests (in shares)	(1,490,999)
Net units issued under the SMLP LTIP (in shares)	0
Units, ending balance (in shares)	0