OPERATING SEGMENT DATA - Operating Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
OPERATING EXPENSES
Salaries, wages, and benefits	$ 453,283	$ 449,024	$ 892,806	$ 886,101
Fuel, supplies, and expenses	112,137	123,705	221,659	245,880
Depreciation and amortization	36,276	35,811	73,109	70,821
Contingent consideration	3,850	(10,000)	11,170	5,040
(Gain) loss on sale of property and equipment			565	1,188
Other	47,303	47,096	92,770	93,124
Total consolidated operating expenses	1,028,986	1,061,348	2,042,970	2,146,283
Operating Segments | Asset Based
OPERATING EXPENSES
Salaries, wages, and benefits	352,678	344,538	697,677	680,143
Fuel, supplies, and expenses	82,938	90,897	163,982	185,185
Operating taxes and licenses	13,557	14,094	27,086	28,073
Insurance	16,964	12,889	31,446	26,162
Communications and utilities	4,412	4,553	9,211	9,857
Depreciation and amortization	26,646	25,273	53,653	50,184
Rents and purchased transportation	70,315	101,922	135,986	192,666
Shared services	72,245	74,468	137,159	139,081
(Gain) loss on sale of property and equipment	(91)	416	58	365
Innovative technology costs		8,343		14,411
Other	269	1,297	1,686	2,909
Total consolidated operating expenses	639,933	678,690	1,257,944	1,329,036
Operating Segments | Asset-Light
OPERATING EXPENSES
Purchased transportation	339,247	343,102	683,369	713,265
Salaries, wages, and benefits	31,036	32,485	61,340	67,495
Supplies and expenses	2,768	2,905	5,577	6,534
Depreciation and amortization	5,039	5,085	10,117	10,153
Shared services	17,297	16,500	33,571	33,014
Contingent consideration	3,850	(10,000)	11,170	5,040
Other	6,078	6,559	11,792	13,318
Total consolidated operating expenses	405,315	396,636	816,936	848,819
Other and eliminations
OPERATING EXPENSES
Total consolidated operating expenses	$ (16,262)	$ (13,978)	$ (31,910)	$ (31,572)