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

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
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

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

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

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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ 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 fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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

- Definition

The percentage of borrowing availability of the maximum revolver amount.

+ References

No definition available.

+ Details

Name:	usak_AvailabilityPercentageOfMaximumRevolverAmount
Namespace Prefix:	usak_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the borrowing base of a credit facility before any additions pertaining to eligible revenue equipment.

+ References

No definition available.

+ Details

Name:	usak_BorrowingBaseBeforeAdditionsOfEligibleRevenueEquipment
Namespace Prefix:	usak_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the percentage of eligible investment grade accounts receivable elements for calculating the maximum amount of the credit facility.

+ References

No definition available.

+ Details

Name:	usak_BorrowingBasedThresholdEligibleInvestmentGradeAccountsReceivablePercentage
Namespace Prefix:	usak_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of eligible revenue equipment elements for calculating the maximum amount of the credit facility.

+ References

No definition available.

+ Details

Name:	usak_BorrowingBasedThresholdEligibleRevenueEquipmentPercentage
Namespace Prefix:	usak_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of eligible unbilled accounts receivable elements for calculating the maximum amount of the credit facility.

+ References

No definition available.

+ Details

Name:	usak_BorrowingBasedThresholdEligibleUnbilledAccountsReceivablePercentage
Namespace Prefix:	usak_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of newly acquired revenue equipment elements for calculating the maximum amount of the credit facility.

+ References

No definition available.

+ Details

Name:	usak_BorrowingBasedThresholdNewlyAcquiredRevenueEquipmentPercentage
Namespace Prefix:	usak_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of consolidated fixed charge coverage and achievement of certain financial ratios.

+ References

No definition available.

+ Details

Name:	usak_DebtInstrumentCovenantFixedChargeCoverageRatio
Namespace Prefix:	usak_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Additional borrowing capacity of the line of credit facility.

+ References

No definition available.

+ Details

Name:	usak_LineOfCreditFacilityAdditionalBorrowingCapacity
Namespace Prefix:	usak_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents information about the additional borrowing capacity amount.

+ References

No definition available.

+ Details

Name:	usak_LineOfCreditFacilityAdditionalBorrowingCapacityIncrementalAmount
Namespace Prefix:	usak_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The minimum excess availability requirement as a percentage of the maximum revolver amount.

+ References

No definition available.

+ Details

Name:	usak_MinimumExcessAvailabilityPercentageOfMaximumRevolverAmount
Namespace Prefix:	usak_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=usak_LetterOfCreditSubFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=usak_SwingLineSubFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
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Long-term Debt (Details Textual) - USD ($)	Jan. 31, 2019	Mar. 31, 2019	Feb. 15, 2015
Debt Instrument [Line Items]
Borrowing based threshold for eligible unbilled accounts receivable	85.00%
Remaining borrowing capacity		$ 50,000,000
Weighted average interest rate		3.88%
Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 225,000,000		$ 170,000,000
Additional borrowing capacity	75,000,000
Additional borrowing capacity, incremental amount	$ 20,000,000
Debt instrument, term	5 years
Commitment fee percentage	0.25%
Borrowing based threshold eligible investment grade accounts receivable percentage	85.00%
Borrowing base before additions of eligible revenue equipment	$ 10,000,000.0
Newly acquired revenue equipment, percentage	85.00%
Eligible revenue equipment, percentage	85.00%
Fixed charge coverage ratio	1
Minimum excess availability percentage of maximum revolver amount	10.00%
Percentage of maximum revolver amount	10.00%
Letters of credit outstanding, amount		$ 5,400,000
Letter of Credit Sub Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 15,000,000
Swing Line Sub Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 25,000,000
Minimum \| Revolving Credit Facility
Debt Instrument [Line Items]
Borrowing based threshold eligible investment grade accounts receivable percentage	85.00%
Maximum \| Revolving Credit Facility
Debt Instrument [Line Items]
Borrowing based threshold eligible investment grade accounts receivable percentage	90.00%
Base Rate \| Minimum \| Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate	0.25%
Base Rate \| Maximum \| Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate	0.75%
London Interbank Offered Rate (LIBOR) \| Minimum \| Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate	1.25%
London Interbank Offered Rate (LIBOR) \| Maximum \| Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%