A permanent amortization of the revenue equipment portion of the borrowing base.

No definition available.

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

- Definition

Book value of revenue equipment pledged as collateral that must be maintained in excess of the facility size.

+ References

No definition available.

+ Details

Name:	usak_BookValueOfExcessCollateral
Namespace Prefix:	usak_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	usak_LineOfCreditFacilityMinimumExcessAvailability
Namespace Prefix:	usak_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- 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:	usak_Note7LongTermDebtDetailsLineItems
Namespace Prefix:	usak_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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

The maximum amount of borrowing capacity under a line of credit that is available as of the balance sheet date for a specific purpose other than for financing goods acquired for inventory or imminent delivery to a customer.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCapacityAvailableForSpecificPurposeOtherThanForTradePurchases
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://www.xbrl.org/2003/role/presentationRef

-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

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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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 cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585

+ Details

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

Note 7 - Long-Term Debt (Details) (USD $)	0 Months Ended	9 Months Ended
Note 7 - Long-Term Debt (Details) (USD $)	Sep. 30, 2014	Sep. 30, 2014	Aug. 24, 2012
Note 7 - Long-Term Debt (Details) [Line Items]
Minimum Excess Availability, Percentage of Maximum Revolver Amount	15.00%	15.00%
Letters of Credit Outstanding, Amount	$ 3,800,000	$ 3,800,000
Scenario, Forecast [Member] \| Revolving Credit Facility [Member] \| Maximum [Member]
Note 7 - Long-Term Debt (Details) [Line Items]
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases	73,500,000	73,500,000
Additional Restrictions [Member] \| Revolving Credit Facility [Member] \| Maximum [Member]
Note 7 - Long-Term Debt (Details) [Line Items]
Book Value Of Excess Collateral	20,000,000	20,000,000
Revolver [Member] \| Letter of Credit [Member]
Note 7 - Long-Term Debt (Details) [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	15,000,000	15,000,000
Revolving Credit Facility [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Minimum [Member]
Note 7 - Long-Term Debt (Details) [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.25%
Revolving Credit Facility [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Maximum [Member]
Note 7 - Long-Term Debt (Details) [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.75%
Revolving Credit Facility [Member] \| Minimum [Member]
Note 7 - Long-Term Debt (Details) [Line Items]
Book Value Of Excess Collateral	30,000,000	30,000,000
Revolving Credit Facility [Member]
Note 7 - Long-Term Debt (Details) [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			125,000,000
Line of Credit Facility, Additional Borrowing Capacity	50,000,000	50,000,000
Line of Credit Facility, Minimum Excess Availability	18,800,000	18,800,000
Book Value Of Excess Collateral	42,800,000	42,800,000
Amortization of Borrowing Base		1,600,000
Proceeds from Long-term Lines of Credit	0
Debt, Weighted Average Interest Rate	2.50%	2.50%
Line of Credit Facility, Remaining Borrowing Capacity	$ 38,900,000	$ 38,900,000