v3.19.1

Financial Highlights (Net Asset Value Based Total Return for a Shareholder) (Details) | 3 Months Ended
--- | ---
Mar. 31, 2018
Investment Company, Financial Highlights [Abstract] |
Total Return | 4.30%

X
- References No definition available. + Details
Name: | us-gaap_InvestmentCompanyFinancialHighlightsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition 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). + References 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 + Details
Name: | us-gaap_InvestmentCompanyTotalReturnAfterIncentiveFees
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration