Condensed Consolidated Statements of Operations (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income Statement [Abstract]
Revenues	$ 331,908	$ 262,546	$ 631,288	$ 499,119
Operating expenses:
Purchased transportation costs	227,922	185,875	434,264	352,905
Personnel and related benefits	36,670	28,963	71,526	55,696
Other operating expenses	38,782	26,940	74,472	53,012
Depreciation and amortization	3,846	2,125	7,201	4,085
Acquisition transaction expenses	290	70	290	208
Total operating expenses	307,510	243,973	587,753	465,906
Operating income	24,398	18,573	43,535	33,213
Interest expense:
Interest on long-term debt	1,610	2,071	3,485	3,869
Dividends on preferred stock subject to mandatory redemption	0	0	0	49
Total interest expense	1,610	2,071	3,485	3,918
Income before provision for income taxes	22,788	16,502	40,050	29,295
Provision for income taxes	8,818	6,302	15,498	11,164
Net income available to common stockholders	$ 13,970	$ 10,200	$ 24,552	$ 18,131
Earnings per share available to common stockholders:
Basic	$ 0.39	$ 0.33	$ 0.70	$ 0.59
Diluted	$ 0.37	$ 0.32	$ 0.67	$ 0.56
Weighted average common stock outstanding:
Basic	35,585	30,821	35,289	30,782
Diluted	37,307	32,186	36,442	32,182