Investments - Schedule of Purchase Price Allocation of Properties (Details) (Parenthetical) $ in Millions	9 Months Ended
Sep. 30, 2020 USD ($)
Real Estate Investment Property Net [Abstract]
Acquisition related costs and acquired working capital	$ 10.4

Business combination acquisition related costs and acquired working capital.

No definition available.

Name:	ck0001711929_BusinessCombinationAcquisitionRelatedCostsAndAcquiredWorkingCapital
Namespace Prefix:	ck0001711929_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration