OPERATING SEGMENT DATA - Operating Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
OPERATING EXPENSES
Salaries, wages, and benefits			$ 1,781,304	$ 1,728,653	$ 1,527,533
Fuel, supplies, and expenses			479,688	488,009	360,657
Depreciation and amortization			145,349	138,159	122,560
Contingent consideration			(19,100)	18,300
Lease impairment charges	$ 30,200		30,162
Gain on sale of subsidiary				(402)	(6,923)
Other			194,752	160,698	129,351
Total consolidated operating expenses			4,254,824	4,634,482	3,489,207
Gain on sale of property and equipment			(4,797)	11,650	8,520
Increase in fair value of equity investment		$ 3,700	3,739
Operating Segments | Asset Based
OPERATING EXPENSES
Salaries, wages, and benefits			1,379,756	1,293,487	1,198,253
Fuel, supplies, and expenses			361,355	378,558	266,139
Operating taxes and licenses			55,918	52,290	49,461
Insurance			52,025	47,382	37,800
Communications and utilities			19,288	18,949	18,773
Depreciation and amortization			104,165	97,322	93,799
Rents and purchased transportation			338,575	441,167	364,345
Shared services			279,248	281,698	263,532
(Gain) loss on sale of property and equipment and lease impairment charges			982	(12,468)	(8,676)
Lease impairment charges			700
Innovative technology costs			21,711	27,207	27,631
Other			4,829	4,175	2,009
Total consolidated operating expenses			2,617,852	2,629,767	2,313,066
Noncash gain on a like-kind property exchange of a service center				(4,300)
Operating Segments | Asset Based | Land and structures
OPERATING EXPENSES
Gain on sale of property and equipment					8,600
Operating Segments | Asset-Light
OPERATING EXPENSES
Purchased transportation			1,435,604	1,784,668	1,097,332
Supplies and expenses			12,094	13,955	8,661
Depreciation and amortization			20,370	20,730	11,387
Shared services			194,296	218,133	132,137
Contingent consideration			(19,100)	18,300
Lease impairment charges			14,407
Legal settlement			9,500
Gain on sale of subsidiary				(402)	(6,923)
Other			25,745	31,163	11,635
Total consolidated operating expenses			1,692,916	2,086,547	1,254,229
Other and eliminations
OPERATING EXPENSES
Depreciation and amortization			20,814	20,107	17,374
Lease impairment charges			15,100
Total consolidated operating expenses			$ (55,944)	$ (81,832)	$ (78,088)