Financial Highlights (Net Asset Value Based Total Return for a Shareholder) (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018
Investment Company, Financial Highlights [Abstract]
Total Return	1.10%	9.43%

Percentage increase (decrease), after deduction of incentive fee, in fund net asset value. Includes, but is not limited to, interest and dividend income (loss) and realized and unrealized gain (loss).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 205
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=25866437&loc=d3e10421-115837

Name:	us-gaap_InvestmentCompanyTotalReturnAfterIncentiveFees
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration