Long-term Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Long-term debt [Abstract]
Borrowings under credit facility	$ 26,215,000		$ 19,888,000
Notes payable	17,441,000		7,989,000
Capitalized lease obligations	2,490,000		2,848,000
Total long-term debt	46,146,000		30,725,000
Less: Current maturities	(3,040,000)		(1,936,000)
Total maturities due after one year	43,106,000		28,789,000
Aggregate availability of credit facility	50,000,000
Maturity date of credit facility	Mar. 29, 2015
Borrowing base availability under the credit facility	46,200,000
Remaining borrowing availability under credit facility	14,600,000
Stand by letters of credit issued	5,400,000
Line of Credit Facility [Line Items]
Basis spread on Federal Funds Rate (in hundredths)	0.50%
Term of interest period for LIBOR	30 days
Basis spread on LIBOR (in hundredths)	1.00%
Number of days interest will accrue	1 day
Interest expense on credit facility	(1,649,000)		(844,000)	(470,000)
Master security agreement funds used to purchase revenue equipment	22,600,000
Effective percentage rate on promissory note, range, minimum (in hundredths)	4.40%
Effective percentage rate on promissory note, range , maximum (in hundredths)	7.90%
Revenue generating equipment under capital lease	3,000,000
Term of rental agreement for capital lease obligation (in months)	P60M
Effective interest rate on the capital lease (in hundredths)	6.80%
Interest expense, debt on notes payable and capital lease obligation	722,000		189,000
Aggregate Maturities of Long-Term Debt [Abstract]
2013	3,040,000
2014	3,148,000
2015	29,040,000	[1]
2016	4,209,000
2017	1,305,000
Thereafter	5,404,000
Total	46,146,000
Obligation related to amount borrowed under the credit facility	26,215,000		19,888,000
LIBOR Loan [Member]
Line of Credit Facility [Line Items]
Interest rate of loans outstanding under credit facility (in hundredths)	2.80%
Bank Base Rate Loan [Member]
Line of Credit Facility [Line Items]
Interest rate of loans outstanding under credit facility (in hundredths)	4.80%
Credit Facility [Member]
Line of Credit Facility [Line Items]
Interest expense on credit facility	$ 774,000		$ 577,000	$ 58,000

[1] $26.2 million of this amount represents borrowings under our credit facility, which matures March 2015.