OPERATING SEGMENT DATA - Operating Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
OPERATING EXPENSES
Salaries, wages, and benefits	$ 449,024	$ 442,875	$ 886,006	$ 857,780
Fuel, supplies, and expenses	124,148	129,505	246,766	239,864
Depreciation and amortization	35,811	34,884	70,821	69,280
Contingent consideration	(10,000)		5,040	810
Gain on sale of subsidiary				(402)
(Gain) loss on sale of property and equipment			1,188	(4,073)
Other	46,653	40,152	92,333	76,981
Total consolidated operating expenses	1,061,348	1,185,654	2,146,283	2,360,802
Operating Segments | Asset Based
OPERATING EXPENSES
Salaries, wages, and benefits	344,538	328,068	680,143	641,565
Fuel, supplies, and expenses	90,897	99,296	185,185	184,127
Operating taxes and licenses	14,094	12,823	28,073	25,316
Insurance	12,889	12,197	26,162	22,628
Communications and utilities	4,553	4,648	9,857	9,335
Depreciation and amortization	25,273	24,463	50,184	48,768
Rents and purchased transportation	101,922	121,550	192,666	224,535
Shared services	74,468	75,584	139,081	142,734
(Gain) loss on sale of property and equipment	416	(1,370)	365	(4,065)
Innovative technology costs	8,343	7,954	14,411	14,914
Other	1,297	753	2,909	1,386
Total consolidated operating expenses	678,690	685,966	1,329,036	1,311,243
Operating Segments | Asset-Light
OPERATING EXPENSES
Purchased transportation	343,102	448,160	713,265	956,540
Supplies and expenses	3,348	4,263	7,420	7,529
Depreciation and amortization	5,085	5,468	10,153	10,648
Shared services	48,985	57,986	100,414	108,183
Contingent consideration	(10,000)		5,040	810
Gain on sale of subsidiary		(402)		(402)
Other	6,116	6,701	12,527	13,036
Total consolidated operating expenses	396,636	522,176	848,819	1,096,344
Other and eliminations
OPERATING EXPENSES
Total consolidated operating expenses	$ (13,978)	$ (22,488)	$ (31,572)	$ (46,785)