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

Term of lessee's finance lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeFinanceLeaseTermOfContract1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
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

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

+ 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_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

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: 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(a)(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 3: 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 4: 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

+ Details

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

- Definition

The accrued insurance premium payable to third-party financing companies.

+ References

No definition available.

+ Details

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

- 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

Percentage of original cost at which the Company has the option to purchase at the end of the lease.

+ References

No definition available.

+ Details

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

- Definition

The initial monthly payment in a sale-leaseback transaction.

+ References

No definition available.

+ Details

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

- Definition

The amount of increase decrease in long-term debt borrowing capacity.

+ References

No definition available.

+ Details

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

- 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 amount of the maximum increase available that is subject to lender approval.

+ References

No definition available.

+ Details

Name:	usak_LineOfCreditFacilityMaximumIncreaseAvailableSubjectToLenderApproval
Namespace Prefix:	usak_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

- Definition

The proceeds from obligation under finance lease.

+ References

No definition available.

+ Details

Name:	usak_ProceedsFromObligationUnderFinanceLease
Namespace Prefix:	usak_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_TrucksMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=usak_ObligationsUnderFinanceLeaseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
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_CreditFacilityAxis=usak_SwingLineSubFacilityMember
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_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
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=usak_InsurancePremiumsFinancingNoteMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

DEBT - Other (Details) - USD ($)			1 Months Ended		6 Months Ended
DEBT - Other (Details) - USD ($)	Jan. 31, 2019	Feb. 15, 2015	Jul. 31, 2019	Apr. 30, 2019	Jun. 30, 2019	Jun. 30, 2020	Apr. 20, 2020	Dec. 31, 2019	Oct. 31, 2019
Debt Instruments
Long-term debt						$ 95,222,000		$ 89,514,000
Borrowing based threshold for eligible unbilled accounts receivable (as a percent)	85.00%
Remaining borrowing capacity						$ 38,000,000
Weighted average interest rate						2.90%
Proceeds from obligation under finance lease			$ 2,300,000		$ 10,471,000
Finance lease contract term			5 years
Initial monthly payment in sale-leaseback transaction			$ 30,000.00
Tractors
Debt Instruments
Proceeds from obligation under finance lease				$ 10,500,000
Finance lease contract term				5 years
Initial monthly payment in sale-leaseback transaction				$ 100,000
Percentage of original cost at which Company has option to purchase at end of lease				32.50%
Sale leaseback finance obligations
Debt Instruments
Long-term debt						$ 10,731,000		11,783,000
Credit Facility
Debt Instruments
Long-term debt	$ 225,000,000.0	$ 170,000,000.0				83,075,000	$ 170,000,000.0	73,225,000
Maximum increase available subject to lender approval	75,000,000.0
Excercisable, incremental borrowing capacity	$ 20,000,000.0
Term of debt instrument	5 years	5 years
Increase (decrease) in borrowing capacity							$ (55,000,000.0)
Fixed charge coverage ratio	1.0
Commitment fee percentage	0.25%
Borrowing base before additions of eligible revenue equipment	$ 10,000,000.0
Newly acquired revenue equipment (as a percent)	85.00%
Eligible revenue equipment (as a percent)	85.00%
Percentage of maximum revolver amount	10.00%
Minimum excess availability percentage of maximum revolver amount	20.00%
Letter of credit outstanding						7,400,000
Credit Facility \| Minimum
Debt Instruments
Borrowing based threshold eligible investment grade accounts receivable (as a percent)	85.00%
Credit Facility \| Maximum
Debt Instruments
Borrowing based threshold eligible investment grade accounts receivable (as a percent)	90.00%
Swingline sub-facility
Debt Instruments
Long-term debt	$ 25,000,000.0					0
Letter of credit sub-facility
Debt Instruments
Long-term debt	$ 15,000,000.0
Base Rate \| Credit Facility \| Minimum
Debt Instruments
Basis spread on variable rate (as a percent)	0.25%
Base Rate \| Credit Facility \| Maximum
Debt Instruments
Basis spread on variable rate (as a percent)	0.75%
London Interbank Offered Rate (LIBOR) \| Credit Facility \| Minimum
Debt Instruments
Basis spread on variable rate (as a percent)	1.25%
London Interbank Offered Rate (LIBOR) \| Credit Facility \| Maximum
Debt Instruments
Basis spread on variable rate (as a percent)	1.75%
Insurance Premiums Financing Note
Debt Instruments
Accrued Premium Insurance Payable									$ 4,500,000
Insurance Premiums Financing Note \| Sale leaseback finance obligations
Debt Instruments
Long-term debt						$ 1,416,000		$ 4,506,000