Condensed Consolidated Statements of Operations (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]
Revenues	$ 498,086	$ 363,156	$ 1,340,298	$ 994,444
Operating expenses:
Purchased transportation costs	347,247	253,158	926,600	687,422
Personnel and related benefits	55,533	39,816	148,574	111,342
Other operating expenses	61,781	41,933	174,559	116,405
Depreciation and amortization	6,319	4,029	16,788	11,230
Acquisition transaction expenses	1,926	561	2,305	851
Total operating expenses	472,806	339,497	1,268,826	927,250
Operating income	25,280	23,659	71,472	67,194
Interest expense	3,827	2,078	8,936	5,563
Income before provision for income taxes	21,453	21,581	62,536	61,631
Provision for income taxes	7,040	8,351	22,941	23,849
Net income available to common stockholders	$ 14,413	$ 13,230	$ 39,595	$ 37,782
Earnings per share available to common stockholders:
Basic	$ 0.38	$ 0.36	$ 1.05	$ 1.06
Diluted	$ 0.37	$ 0.35	$ 1.01	$ 1.01
Weighted average common stock outstanding:
Basic	37,920	36,407	37,827	35,666
Diluted	39,380	38,191	39,268	37,469