Derivative Instruments (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 Contract	Dec. 31, 2012
Derivative Instruments Gain Loss [Line Items]
Open commodity contracts	1,849
Variable interest rate on the Term Loan fixed under derivative agreement	0.92%
Variable interest rate for next three years	2015-07
Net position	$ 2,095	$ 416
Interest rate swap
Derivative Instruments Gain Loss [Line Items]
Interest rate swap agreement, outstanding notional amount	4,395	5,245
Fair value of the interest rate swap agreements	37	46
Commodity Contract
Derivative Instruments Gain Loss [Line Items]
Collateral associated with commodity-based derivatives	$ 8,968	$ 8,053