Condensed Consolidated Statements of Earnings (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating revenues	$ 2,280,826	$ 2,089,627
Operating expenses:
Rents and purchased transportation	1,136,151	999,889
Salaries, wages and employee benefits	574,249	516,326
Depreciation and amortization	130,095	119,930
Fuel and fuel taxes	101,123	112,125
Operating supplies and expenses	85,598	78,172
General and administrative expenses, net of asset dispositions	45,165	45,038
Insurance and claims	32,361	28,994
Operating taxes and licenses	13,312	13,160
Communication and utilities	8,031	8,198
Total operating expenses	2,126,085	1,921,832
Operating income	154,741	167,795
Net interest expense	12,036	13,033
Earnings before income taxes	142,705	154,762
Income taxes	37,871	35,161
Net earnings	$ 104,834	$ 119,601
Weighted average basic shares outstanding (in shares)	105,985	108,730
Basic earnings per share (in dollars per share)	$ 0.99	$ 1.10
Weighted average diluted shares outstanding (in shares)	106,950	109,664
Diluted earnings per share (in dollars per share)	$ 0.98	$ 1.09
Dividends declared per common share (in dollars per share)	$ 0.27	$ 0.26
Service Excluding Fuel Surcharge [Member]
Operating revenues	$ 2,045,694	$ 1,855,341
Fuel Surcharge [Member]
Operating revenues	$ 235,132	$ 234,286