Condensed Consolidated Statements of Operations (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]
Revenues	$ 363,156	$ 279,165	$ 994,444	$ 778,284
Operating expenses:
Purchased transportation costs	253,158	196,042	687,422	548,947
Personnel and related benefits	39,816	30,331	111,342	86,027
Other operating expenses	41,933	31,883	116,405	84,895
Depreciation and amortization	4,029	2,424	11,230	6,509
Acquisition transaction expenses	561	480	851	688
Total operating expenses	339,497	261,160	927,250	727,066
Operating income	23,659	18,005	67,194	51,218
Interest expense:
Interest on long-term debt	2,078	1,943	5,563	5,812
Dividends on preferred stock subject to mandatory redemption	0	0	0	49
Total interest expense	2,078	1,943	5,563	5,861
Income before provision for income taxes	21,581	16,062	61,631	45,357
Provision for income taxes	8,351	6,190	23,849	17,354
Net income available to common stockholders	$ 13,230	$ 9,872	$ 37,782	$ 28,003
Earnings per share available to common stockholders:
Basic	$ 0.36	$ 0.32	$ 1.06	$ 0.91
Diluted	$ 0.35	$ 0.31	$ 1.01	$ 0.87
Weighted average common stock outstanding:
Basic	36,407	30,859	35,666	30,808
Diluted	38,191	32,260	37,469	32,220