FINANCIAL INSTRUMENTS, OFF-BALANCE SHEET RISKS AND CONTINGENCIES (Additional Information) (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Carrying Amounts and Fair Values of Financial Instruments or Liabilities [Line Items]
Cash investments in money market funds	$ 17,000,000
Deposits in domestic and foreign financial institutions	$ 46,188,610	$ 66,728,725

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of deposits in accounts that offer many of the same services as checking accounts although transactions may be somewhat more limited, share some of the characteristics of a money market fund and are insured by the Federal government, also known as money market accounts.

+ References

+ Details

Name:	us-gaap_DepositsMoneyMarketDeposits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying Amounts and Fair Values of Financial Instruments or Liabilities [Line Items]

+ References

No definition available.

+ Details

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Namespace Prefix:	usl_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration