Long-term Debt (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Long-term debt [Abstract]
Borrowings under credit facility	$ 25,839,000	$ 26,215,000
Notes payable	16,801,000	17,441,000
Capitalized lease obligations	2,396,000	2,490,000
Total long-term debt	45,036,000	46,146,000
Less: Current maturities	(3,102,000)	(3,040,000)
Total maturities due after one year	41,934,000	43,106,000
Aggregate availability of credit facility	50,000,000
Maturity date of credit facility	Mar. 29, 2015
Borrowing base availability under the credit facility	42,100,000
Standby letters of credit issued	6,600,000
Remaining borrowing availability under credit facility	9,700,000
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
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 under capital lease obligation	60 months
Effective interest rate on the capital lease (in hundredths)	6.80%
LIBOR Loan [Member]
Line of Credit Facility [Line Items]
Interest rate of loans outstanding under credit facility (in hundredths)	3.00%
Bank Base Rate Loan [Member]
Line of Credit Facility [Line Items]
Interest rate of loans outstanding under credit facility (in hundredths)	5.00%