Derivative Instruments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014 MMcf	Sep. 30, 2014 Commodity Contract [Member] Accrued Liabilities [Member]	Sep. 30, 2014 Commodity Contract [Member] Other Liabilities [Member]	Sep. 30, 2014 Commodity Contract [Member] Assets, Total [Member]	Sep. 30, 2014 Commodity Contract [Member] Liabilities, Total [Member]	Sep. 30, 2014 Commodity Contract [Member] Prepaid Expenses [Member]	Sep. 30, 2014 Commodity Contract [Member] Other Assets [Member]	Dec. 31, 2013 Natural Gas [Member] Swap [Member]	Dec. 31, 2013 Natural Gas [Member] Swap [Member] Other Accrued Liabilities [Member]	Dec. 31, 2013 Natural Gas [Member] Swap [Member] Other Liabilities [Member]	Dec. 31, 2013 Natural Gas [Member] Swap [Member] Prepaid Expenses [Member]	Dec. 31, 2013 Natural Gas [Member] Swap [Member] Other Assets [Member]
Derivative [Line Items]
Derivative Liability, Current		$ 7,204
Derivative Liability, Noncurrent			1,350							5,885
Derivative, Nonmonetary Notional Amount	199,600
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	14,853
Derivative Asset, Fair Value, Gross Asset				51,710				83,661
Derivative Liability, Fair Value, Gross Liability					8,554			18,212
Derivative Asset, Current						31,520			12,327		59,605
Derivative Asset, Noncurrent							$ 20,190					$ 24,056