Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Statement of Comprehensive Income [Abstract]
Operating revenues	$ 5,674.3	$ 5,290.5	$ 5,498.9
Operating expenses:
Purchased transportation	1,980.0	1,991.3	2,184.5
Salaries, wages, and benefits	1,595.0	1,409.7	1,359.1
Fuel and fuel taxes	434.5	398.2	437.4
Depreciation and amortization	450.0	413.7	382.5
Operating supplies and expenses—net	725.3	636.5	576.0
Insurance and related expenses	187.4	151.5	114.3
Other general expenses	133.2	124.4	148.7
Total operating expenses	5,505.4	5,125.3	5,202.5
Income from operations	168.9	165.2	296.4
Other expenses (income):
Interest income	(5.9)	(4.3)	(7.0)
Interest expense	33.8	16.6	14.2
Other expenses (income)—net	3.0	0.7	(16.9)
Total other expenses (income)—net	30.9	13.0	(9.7)
Income before income taxes	138.0	152.2	306.1
Provision for income taxes	34.4	35.2	67.6
Net income	103.6	117.0	238.5
Other comprehensive income (loss):
Foreign currency translation adjustment—net	0.6	(0.9)	0.5
Net unrealized gains on marketable securities—net of tax	1.3	0.5	1.1
Total other comprehensive income (loss)—net	1.9	(0.4)	1.6
Comprehensive income	$ 105.5	$ 116.6	$ 240.1
Weighted average common shares outstanding	175.2	175.5	177.3
Basic earnings per share	$ 0.59	$ 0.67	$ 1.35
Weighted average diluted shares outstanding	175.9	176.1	178.2
Diluted earnings per share	$ 0.59	$ 0.66	$ 1.34
Dividends declared per share	$ 0.38	$ 0.38	$ 0.36