Summary of Significant Accounting Policies (Details 5) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011	Dec. 31, 2010
Income Taxes
Number of wholly owned subsidiary subject to federal tax	3
Ownership interest (as a percent)	100.00%
Net operating loss carried forward	$ 6,916
Expiry Period for Net Operating Loss Carry Forwards	20 years
Effective Texas Margin Tax, rate (as a percent)	0.70%
Provision for Texas Margin Tax	$ 1,654	$ 1,453	$ 895
Maximum
Risk Management
Forward natural gas contract, term	5 years
Minimum
Risk Management
Forward natural gas contract, term	1 year