ACQUISITIONS (Details)				3 Months Ended		9 Months Ended		108 Months Ended
	Sep. 01, 2017 USD ($)	Jul. 01, 2017 USD ($) shares	May 01, 2017 USD ($) shares	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) item	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Number of open-deck trucking companies acquired | item								12
Allocation of the purchase price paid to the fair values of the net assets
Goodwill				$ 139,889,000		$ 139,889,000		$ 139,889,000	$ 89,035,000
Business Acquisition, Pro Forma Information [Abstract]
Pro forma revenue				241,135,000	$ 230,092,000	690,449,000	$ 666,014,000
Pro forma net income				$ 285,000	$ (1,167,000)	$ (11,323,000)	$ 810,000
R&R Trucking Holdings, LLC
Business Acquisition [Line Items]
Voting interest acquired (as a percent)	100.00%
Total consideration paid	$ 38,400,000
Cash payments for business consideration	24,600,000
Outstanding debt assumed	13,800,000
Allocation of the purchase price paid to the fair values of the net assets
Accounts receivable	5,129,000
Prepaid and other current assets	1,515,000
Parts supplies	149,000
Property and equipment	16,887,000
Goodwill	22,560,000
Other long-term assets	156,000
Deferred tax liabilities	(5,238,000)
Accounts payable and other liabilities	(2,920,000)
Total	38,238,000
Transaction expenses incurred, not deductible for taxes purposes	$ 400,000
The Steelman Companies
Business Acquisition [Line Items]
Voting interest acquired (as a percent)		100.00%
Total consideration paid		$ 18,800,000
Cash payments for business consideration		$ 11,200,000
Number of shares transferred | shares		746,170
Recognized Identifiable Assets Acquired And Liabilities Assumed Intangible Assets		$ 13,000,000
Equity transferred		7,600,000
Allocation of the purchase price paid to the fair values of the net assets
Accounts receivable		4,383,000
Prepaid and other current assets		2,296,000
Parts supplies		90,000
Property and equipment		11,100,000
Goodwill		14,318,000
Other long-term assets		5,013,000
Deferred tax liabilities		(2,763,000)
Accounts payable and other liabilities		(15,612,000)
Total		18,825,000
Transaction expenses incurred, not deductible for taxes purposes		$ 300,000
Schilli Transportation Services Inc
Business Acquisition [Line Items]
Voting interest acquired (as a percent)			100.00%
Total consideration paid			$ 27,400,000
Cash payments for business consideration			$ 21,000,000
Number of shares transferred | shares			232,885
Equity transferred			$ 2,300,000
Outstanding debt assumed			4,000,000
Allocation of the purchase price paid to the fair values of the net assets
Accounts receivable			8,798,000
Prepaid and other current assets			4,701,000
Parts supplies			1,681,000
Property and equipment			41,423,000
Goodwill			12,989,000
Deferred tax liabilities			(14,598,000)
Accounts payable and other liabilities			(27,634,000)
Total			27,360,000
Transaction expenses incurred, not deductible for taxes purposes			$ 400,000
Big Freight Systems Inc
Business Acquisition [Line Items]
Voting interest acquired (as a percent)			100.00%
Total consideration paid			$ 16,700,000
Cash payments for business consideration			$ 12,400,000
Number of shares transferred | shares			109,248
Equity transferred			$ 1,100,000
EBITDA multiplier			0.4
Contingent liability			1,100,000
Outstanding debt assumed			3,200,000
Allocation of the purchase price paid to the fair values of the net assets
Accounts receivable			4,914,000
Prepaid and other current assets			576,000
Property and equipment			11,492,000
Goodwill			10,551,000
Other long-term assets			121,000
Deferred tax liabilities			(3,571,000)
Accounts payable and other liabilities			(6,294,000)
Total			17,789,000
Transaction expenses incurred, not deductible for taxes purposes			$ 600,000