Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Operating Revenue	$ 317,037	$ 289,911
Operating Expenses:
Salaries, wages and employees’ benefits	180,903	170,266
Purchased transportation	14,775	12,467
Fuel, operating expenses and supplies	63,990	54,040
Operating taxes and licenses	10,582	10,040
Claims and insurance	9,049	8,081
Depreciation and amortization	20,087	17,243
Loss from property disposals, net	132	190
Total operating expenses	299,518	272,327
Operating Income	17,519	17,584
Nonoperating Expenses (Income):
Interest expense	911	963
Other, net	98	(7)
Nonoperating expenses, net	1,009	956
Income Before Income Taxes	16,510	16,628
Income Tax Provision	5,123	6,053
Net Income	$ 11,387	$ 10,575
Weighted average common shares outstanding – basic	25,225	24,998
Weighted average common shares outstanding – diluted	25,971	25,445
Basic Earnings Per Share	$ 0.45	$ 0.42
Diluted Earnings Per Share	$ 0.44	$ 0.42