UNAUDITED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 913,275	$ 933,224	$ 2,767,436	$ 2,665,300
Transportation costs	778,057	818,240	2,372,226	2,358,286
Gross margin	135,218	114,984	395,210	307,014
Costs and expenses:
Salaries and benefits	59,765	57,123	182,652	163,496
General and administrative	30,906	19,327	77,852	55,557
Depreciation and amortization	7,301	3,800	21,150	11,286
Total costs and expenses	97,972	80,250	281,654	230,339
Operating income	37,246	34,734	113,556	76,675
Other income (expense):
Interest expense	(2,780)	(2,411)	(8,526)	(6,702)
Interest income	613	340	1,581	365
Other, net	56	251	(14)	20
Total other expense	(2,111)	(1,820)	(6,959)	(6,317)
Income from continuing operations before income taxes	35,135	32,914	106,597	70,358
Provision for income taxes	9,030	7,150	27,381	16,371
Income from continuing operations	26,105	25,764	79,216	53,987
Income from discontinued operations, net of income taxes		88,846		98,842
Net income	26,105	114,610	79,216	152,829
Other comprehensive income:
Foreign currency translation adjustments	(33)	22	(29)	26
Total comprehensive income	$ 26,072	$ 114,632	$ 79,187	$ 152,855
Earnings per share from continuing operations
Basic	$ 0.79	$ 0.77	$ 2.37	$ 1.62
Diluted	0.78	0.77	2.36	1.61
Earnings per share from discontinued operations
Basic		2.66		2.96
Diluted		2.64		2.95
Earnings per share net income
Basic	0.79	3.43	2.37	4.58
Diluted	$ 0.78	$ 3.41	$ 2.36	$ 4.56
Basic weighted average number of shares outstanding	33,034	33,399	33,385	33,387
Diluted weighted average number of shares outstanding	33,265	33,605	33,522	33,548