DEBT - Other (Details) - USD ($) $ in Thousands		1 Months Ended
	Jan. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Oct. 31, 2021	Sep. 30, 2021	Dec. 31, 2020	Oct. 31, 2020	Apr. 20, 2020
Debt Instruments
Long-term debt					$ 69,873	$ 88,143
Borrowing based threshold for eligible unbilled accounts receivable (as a percent)	85.00%
Remaining borrowing capacity					$ 96,300
Weighted average interest rate					1.54%
Finance lease contract term		5 years
Initial monthly payment in sale-leaseback transaction		$ 30
Tractors
Debt Instruments
Proceeds from obligation under finance lease		$ 2,300	$ 10,500
Finance lease contract term			5 years
Initial monthly payment in sale-leaseback transaction			$ 100
Percentage of original cost at which Company has option to purchase at end of lease			32.50%
Obligations Under Finance Lease
Debt Instruments
Long-term debt					$ 8,663	9,913
Revolving Credit Facility
Debt Instruments
Long-term debt	$ 225,000				61,000	$ 73,025		$ 170,000
Maximum increase available subject to lender approval	75,000
Exercisable, incremental borrowing capacity	$ 20,000
Term of debt instrument	5 years
Increase (decrease) in borrowing capacity								$ (55,000)
Fixed charge coverage ratio	1.0
Commitment fee percentage	0.25%
Borrowing base before additions of eligible revenue equipment	$ 10,000
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					7,900
Revolving Credit Facility | Minimum
Debt Instruments
Borrowing based threshold eligible investment grade accounts receivable (as a percent)	85.00%
Revolving 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				$ 100
Letter of credit sub-facility
Debt Instruments
Long-term debt	$ 15,000
Base Rate | Revolving Credit Facility | Minimum
Debt Instruments
Basis spread on variable rate (as a percent)	0.25%
Base Rate | Revolving Credit Facility | Maximum
Debt Instruments
Basis spread on variable rate (as a percent)	0.75%
London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | Minimum
Debt Instruments
Basis spread on variable rate (as a percent)	1.25%
London Interbank Offered Rate (LIBOR) | Revolving 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				$ 5,500			$ 5,100