Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: 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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

The periodic payments of principal required on the debt instrument, specified as a percentage of the original face amount plus any additional amount borrowed.

+ References

No definition available.

+ Details

Name:	usx_DebtInstrumentPeriodicPaymentPrincipalAsPercentageOfOriginalFaceAmount
Namespace Prefix:	usx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added as a quarterly adjustment to the basis spread on the variable rate.

+ References

No definition available.

+ Details

Name:	usx_DebtInstrumentQuarterlyAdjustmentToBasisSpreadOnVariableRate
Namespace Prefix:	usx_
Data Type:	num:percentItemType
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Period Type:	duration

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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Long-term Debt - Other information (Details) - USD ($) $ in Millions	4 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2019	Jun. 30, 2018
Debt Instrument [Line Items]
Letters of credit outstanding		$ 31.7	$ 31.7
Credit Facility [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Commitment fee, as a percent		0.25%
Credit Facility [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Commitment fee, as a percent		0.35%
Credit Facility [Member] \| Base Rate Loans [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Quarterly adjustment to rate, as a percent			0.75%
Credit Facility [Member] \| Base Rate Loans [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Quarterly adjustment to rate, as a percent			1.50%
Credit Facility [Member] \| Base Rate Loans [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Basis spread on variable rate, as a percent	1.25%
Credit Facility [Member] \| Eurodollar Rate Loans [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Quarterly adjustment to rate, as a percent			1.75%
Credit Facility [Member] \| Eurodollar Rate Loans [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Quarterly adjustment to rate, as a percent			2.50%
Credit Facility [Member] \| Eurodollar Rate Loans [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate, as a percent	2.25%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowing capacity		$ 150.0	$ 150.0	$ 150.0
Letters of credit outstanding		31.7	31.7
Amount available to borrow		115.4	115.4
Amount outstanding		2.9	2.9
Letter of Credit [Member]
Debt Instrument [Line Items]
Borrowing capacity		75.0	75.0
Swingline Facility [Member]
Debt Instrument [Line Items]
Borrowing capacity		15.0	15.0
Term Facility [Member]
Debt Instrument [Line Items]
Borrowing capacity				$ 200.0
Amount outstanding		$ 187.5	187.5
Term Facility [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Periodic payment, as a percentage of face amount		1.25%
Term Facility [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Periodic payment, as a percentage of face amount		2.50%
Accordion Facility [Member]
Debt Instrument [Line Items]
Borrowing capacity		$ 75.0	$ 75.0