Long-term Debt - Principal payments under the Energy Credit Agreement (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Debt Disclosure [Abstract]
Remainder of 2013	$ 2,500
2014	10,000
2015	10,000
2016	10,000
2017	10,000
2018	25,000
Total	67,500
Less current portion	10,000	4,000
Total long-term debt	$ 57,500	$ 9,000