(Goodwill acquired in business combination by reportable segment) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Rollforward of goodwill by reportable segment
Goodwill beginning balance	$ 442,143	$ 364,687
Adjustments to goodwill for purchase accounting	(2,046)
Acquisition during the year	78,646	77,456
Goodwill closing balance	518,743	442,143
LTL
Rollforward of goodwill by reportable segment
Goodwill beginning balance	197,456	185,406
Adjustments to goodwill for purchase accounting	(144)
Acquisition during the year	0	12,050
Goodwill closing balance	197,312	197,456
TL
Rollforward of goodwill by reportable segment
Goodwill beginning balance	202,547	143,575
Adjustments to goodwill for purchase accounting	(1,906)
Acquisition during the year	10,772	58,972
Goodwill closing balance	211,413	202,547
TMS
Rollforward of goodwill by reportable segment
Goodwill beginning balance	42,140	35,706
Adjustments to goodwill for purchase accounting	4
Acquisition during the year	67,874	6,434
Goodwill closing balance	$ 110,018	$ 42,140