UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($)
Statement Of Cash Flows [Abstract]
Net of cash	$ 1,475

Proceeds from gain on sale of disposition of assets.

No definition available.

Name:	smlp_ProceedsFromGainOnSaleOfDispositionOfAssets
Namespace Prefix:	smlp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration