Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]
Revenues	$ 1,361,410	$ 1,073,354	$ 843,627
Operating expenses:
Purchased transportation costs	944,275	753,459	620,343
Personnel and related benefits	151,158	119,955	87,178
Other operating expenses	163,452	120,718	83,625
Depreciation and amortization	16,311	9,499	4,978
Acquisition transaction expenses	851	773	1,368
Total operating expenses	1,276,047	1,004,404	797,492
Operating income	85,363	68,950	46,135
Interest expense:
Interest on long-term debt	7,883	7,981	4,135
Dividends on preferred stock subject to mandatory redemption	0	49	200
Total interest expense	7,883	8,030	4,335
Income before provision for income taxes	77,480	60,920	41,800
Provision for income taxes	28,484	23,390	15,929
Net income available to common stockholders	$ 48,996	$ 37,530	$ 25,871
Earnings per share available to common stockholders:
Basic (in usd per share)	$ 1.36	$ 1.21	$ 0.85
Diluted (in usd per share)	$ 1.29	$ 1.16	$ 0.82
Weighted average common stock outstanding:
Basic (shares)	36,133	31,040	30,432
Diluted (shares)	37,913	32,425	31,545