Condensed Consolidated Statements of Earnings (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating revenues, excluding fuel surcharge revenues	$ 1,657,380	$ 1,538,701	$ 4,670,200	$ 4,448,709
Fuel surcharge revenues	185,954	151,958	529,208	385,688
Total operating revenues	1,843,334	1,690,659	5,199,408	4,834,397
Operating expenses:
Rents and purchased transportation	947,145	846,238	2,624,707	2,381,547
Salaries, wages and employee benefits	408,340	374,517	1,178,524	1,108,997
Depreciation and amortization	95,959	91,001	281,198	269,717
Fuel and fuel taxes	87,006	74,179	246,725	205,082
Operating supplies and expenses	67,578	62,191	190,085	173,222
Insurance and claims	26,463	21,862	76,930	58,384
General and administrative expenses, net of asset dispositions	29,389	21,025	74,597	61,570
Operating taxes and licenses	10,744	11,665	32,329	34,156
Communication and utilities	5,738	5,004	16,337	15,063
Total operating expenses	1,678,362	1,507,682	4,721,432	4,307,738
Operating income	164,972	182,977	477,976	526,659
Net interest expense	8,310	6,485	22,521	19,347
Earnings before income taxes	156,662	176,492	455,455	507,312
Income taxes	56,277	67,067	154,499	192,778
Net earnings	$ 100,385	$ 109,425	$ 300,956	$ 314,534
Weighted average basic shares outstanding (in shares)	109,703	112,630	110,066	112,790
Basic earnings per share (in dollars per share)	$ 0.92	$ 0.97	$ 2.73	$ 2.79
Weighted average diluted shares outstanding (in shares)	110,628	113,363	111,154	113,709
Diluted earnings per share (in dollars per share)	$ 0.91	$ 0.97	$ 2.71	$ 2.77
Dividends declared per common share (in dollars per share)	$ 0.23	$ 0.22	$ 0.69	$ 0.66