Long-Term Debt (Details) (USD $)	3 Months Ended	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 17, 2012	Jul. 31, 2013	Aug. 01, 2014	Jan. 24, 2011	May 30, 2008
Line of Credit Facility [Line Items]
Deferred financing costs	$ 300,000	$ 300,000	$ 500,000
Amortization of deferred financing costs		600,000	700,000	900,000
Capitalized financing costs	300,000		100,000	300,000
Interest expense		1,578,000	1,714,000	3,363,000
NuDevco Retail Holdings | Spark HoldCo
Line of Credit Facility [Line Items]
Investment in affiliate transferred							50,000
Other Current Assets
Line of Credit Facility [Line Items]
Deferred financing costs	200,000	200,000	400,000
Other Noncurrent Assets
Line of Credit Facility [Line Items]
Deferred financing costs	100,000	100,000	100,000
Working Capital Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity					70,000,000	80,000,000		150,000,000	177,500,000.0
Working capital facility outstanding			27,500,000
Working capital credit facility outstanding portion paid by affiliate							29,000,000
Letters of credit issued and outstanding	10,700,000	10,700,000	10,000,000				15,000,000
Fees on letters of credit issued and outstanding		400,000	500,000	600,000
Nonutilization fee					0.50%
Interest expense		400,000	300,000	1,300,000
Commitment fee percentage		0.50%
Commitment fee amount		100,000	200,000	500,000
Working Capital Facility | Eurodollar | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate					3.00%	3.00%
Working Capital Facility | Eurodollar | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate					3.75%	3.25%
Working Capital Facility | Base Rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate					2.00%	2.00%
Working Capital Facility | Base Rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate					2.75%	2.25%
Working Capital Facility | Cost of Funds Rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate						2.50%
Working Capital Facility | Cost of Funds Rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate						2.75%
Term Loan
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity					125,000,000			130,000,000	100,000,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity					30,000,000				35,000,000
Revolving Credit Facility | Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, outstanding							10,000,000
Revolving Credit Facility | Senior Secured Revolving Credit Facility | Line of Credit
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity							70,000,000.0
Working capital facility outstanding	33,000,000	33,000,000
Contingent maximum borrowing capacity							$ 120,000,000.0
Reduction to interest rate if facility utilization is less than fifty percent							0.25%
Revolving Credit Facility | Minimum | Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Commitment fee percentage							0.375%
Used capacity fee percentage							2.00%
Revolving Credit Facility | Maximum | Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Commitment fee percentage							0.50%
Used capacity fee percentage							2.50%
Revolving Credit Facility | Eurodollar | Minimum | Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate							2.75%
Revolving Credit Facility | Eurodollar | Maximum | Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate							3.00%
Revolving Credit Facility | Base Rate | Minimum | Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate							1.75%
Revolving Credit Facility | Base Rate | Maximum | Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate							2.00%
Revolving Credit Facility | Cost of Funds Rate | Minimum | Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate							2.25%
Revolving Credit Facility | Cost of Funds Rate | Maximum | Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate							2.50%
Revolving Credit Facility | Base Rate Plus Margin | Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Stated percentage interest rate							2.00%
Letters Of Credit Outstanding More Than Two Business Days | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate		2.00%