QUARTERLY RESULTS (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended								9 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total revenue		$ 403.0	$ 450.4	$ 450.6	$ 433.0	$ 447.0	$ 461.6	$ 376.9	$ 327.6		$ 1,737.0	$ 1,613.1	$ 846.3
Operating expenses:
Impairment			85.6			11.1
Deferred taxes								14.0			(58.0)	(19.8)	(53.5)
Intangible Assets		169.7				255.1					169.7	255.1
Cumulative effect of change in effective tax rate												(12.6)	(46.1)
Salaries, wages and employee benefits		112.1	127.7	124.3	119.1	119.6	114.8	90.7	82.3		483.2	407.4	250.0
Fuel											138.5	141.1	93.7
Operations and maintenance		48.4	56.8	53.1	54.8	55.0	51.5	40.4	34.6		213.1	181.5	118.4
Communications		1.2	1.0	1.2	1.0	0.9	0.9	0.8	0.7		4.4	3.3	2.1
Administrative expenses		20.8	21.4	17.2	16.1	17.1	16.1	13.1	12.2		75.5	58.5	33.2
Sales and marketing		1.3	1.3	1.3	1.2	1.0	1.0	0.8	0.6		5.1	3.4	2.0
Taxes and licenses						4.9	4.7	3.9	3.7		19.2	17.2	11.0
Insurance and claims		11.8	13.4	12.2	12.5	13.5	12.7	10.4	9.2		49.9	45.8	24.0
Acquisition-related transaction expenses						0.2	0.6	1.4	0.4			2.6	3.4
Depreciation		27.0	38.3	39.7	41.5	37.4	36.8	31.7	25.2		146.5	131.1	76.9
Gain on disposition of equipment		(3.1)	(1.0)	(0.7)	(0.4)	(1.7)	(0.9)	(0.5)	(0.1)		(5.2)	(3.2)	(0.7)
Operating Expenses		403.9	767.0	445.9	432.3	455.2	447.7	368.4	319.9
Impairments		6.0	306.8			11.1		2.8			312.8	13.9
Restructuring charges		1.5	6.9								8.4
Total operating expenses											2,049.1	1,591.2	839.3
Total other expense		11.7	14.5	11.8	11.9	13.6	11.0	9.5	8.9		49.9	43.0	32.3
Benefit for income taxes		5.8	(57.8)	(0.7)	(1.9)	(1.7)	0.7	(14.5)	(0.4)		(54.6)	(15.9)	(52.3)
Net income (loss)		(18.4)	(273.3)	(6.4)	(9.3)	(20.1)	2.2	13.5	(0.8)		(307.4)	(5.2)	27.0
Less dividends to convertible preferred stockholders		(1.3)	(1.2)	(1.3)	(1.2)	(1.2)	(1.2)	(1.3)	(1.2)
Net income (loss) available to common stockholders		$ (19.7)	$ (274.5)	$ (7.7)	$ (10.5)	$ (21.3)	$ 1.0	$ 12.2	$ (2.0)		$ (312.4)	$ (10.1)	$ 22.0
Basic earnings (loss) per common share		$ (0.31)	$ (4.25)	$ (0.12)	$ (0.16)	$ (0.33)	$ 0.01	$ 0.20	$ (0.04)		$ (4.86)	$ (0.16)	$ 0.59
Diluted earnings (loss) per common share		$ (0.31)	$ (4.25)	$ (0.12)	$ (0.16)	$ (0.33)	$ 0.01	$ 0.20	$ (0.04)		$ (4.86)	$ (0.16)	$ 0.56
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenues:
Total revenue													$ 846.3
Company freight
Revenues:
Total revenue		$ 186.3	$ 205.2	$ 206.9	$ 206.2	$ 210.2	$ 206.9	$ 160.0	$ 144.6		$ 804.6	$ 721.7	460.8
Operating expenses:
Purchased freight											597.7	588.6	225.3
Owner operator freight
Revenues:
Total revenue		104.3	118.3	121.7	111.0	109.8	122.6	112.6	95.5		455.3	440.5	172.0
Brokerage
Revenues:
Total revenue		71.9	78.6	72.8	71.4	78.0	82.2	60.1	46.1		294.7	266.4	120.9
Logistics
Revenues:
Total revenue		8.5	13.5	13.1	12.4	11.6	11.6	8.9	10.7		47.5	42.8	22.1
Fuel
Revenues:
Total revenue		32.0	34.8	36.1	32.0	37.4	38.3	35.3	30.7		134.9	141.7	70.5
Operating expenses:
Cost of revenue		33.2	34.1	36.2	35.0	37.5	38.9	31.3	33.4
Service
Operating expenses:
Cost of revenue		139.2	155.5	156.4	146.6	158.7	$ 170.6	141.6	$ 117.7
Taxes and licenses		4.5	4.8	$ 5.0	$ 4.9
Plan And Project Pivot [Member]
Operating expenses:
Impairment		6.0	306.8
Restructuring and Related Cost, Cost Incurred to Date		1.5	6.9							$ 6.9	1.5
Restructuring charges			$ 8.4							$ 8.4
Corporate/Eliminations
Revenues:
Total revenue											(21.7)	(14.0)
Operating expenses:
Restructuring charges											2.8
Corporate/Eliminations | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenues:
Total revenue													(6.9)
Corporate/Eliminations | Company freight
Revenues:
Total revenue											(13.9)	(8.8)	(5.3)
Corporate/Eliminations | Owner operator freight
Revenues:
Total revenue											(5.9)	(2.8)	(0.8)
Corporate/Eliminations | Brokerage
Revenues:
Total revenue												(0.9)	(0.2)
Corporate/Eliminations | Logistics
Revenues:
Total revenue											(0.1)	(0.1)
Corporate/Eliminations | Fuel
Revenues:
Total revenue											(1.8)	(1.4)	$ (0.6)
Trade names
Operating expenses:
Impairment								$ 2.8
Intangible Assets		$ 59.1				$ 90.6					$ 59.1	$ 90.6
Trade names | Specialized
Operating expenses:
Impairment	$ 2.8