Derivative Instruments (Narrative) (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Derivative [Line Items]
Partnership's average net asset value	$ 134,000,000	$ 159,000,000
Open interest rate futures, maturity	10 years	10 years
Concentration of credit risk	$ 10,576,972		$ 10,942,019
Maximum [Member]
Derivative [Line Items]
Open interest rate futures, maturity	10 years	10 years

Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13537-108611

Name:	us-gaap_ConcentrationRiskCreditRiskFinancialInstrumentMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration