Organization - Additional Information (Detail)	Dec. 31, 2016
General Partner [Member]
Schedule Of Trading Advisors [Line Items]
Required interest in the equity of each Partnership	1.00%

Proportional equity interest amount of ownership required in each Limited Partnership by a General Partner.

No definition available.

Name:	dwsf_GeneralPartnerRequiredEquityInterestInEachPartnership
Namespace Prefix:	dwsf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant