Segment Reporting - Financial Data for Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total Revenues	$ 128,536	$ 177,749	$ 295,217	$ 420,455
Retail cost of revenues	65,605	158,759	184,428	354,014
Less:
Net asset optimization (expenses) revenues	(82)	(56)	239	2,496
Net, gain (loss) on non-trading derivative instruments	8,121	(35,456)	(16,466)	(54,997)
Current period settlements on non-trading derivatives	9,964	12,769	26,572	20,794
Retail Gross Margin	44,994	41,724	100,455	98,301
Total Assets	372,012		372,012		$ 422,968
Goodwill	120,343		120,343		120,343
Non-trading
Less:
Net, gain (loss) on non-trading derivative instruments	7,964	(35,466)	(16,569)	(55,269)
Current period settlements on non-trading derivatives	10,055	12,788	26,664	20,913
Operating Segments | Retail Electricity
Segment Reporting Information [Line Items]
Total Revenues	112,255	160,776	234,023	342,868
Retail cost of revenues	59,268	148,187	159,651	314,074
Less:
Net asset optimization (expenses) revenues	0	0	0	0
Retail Gross Margin	35,573	33,614	66,379	63,588
Total Assets	2,732,318		2,732,318		2,524,884
Goodwill	117,813		117,813		117,813
Operating Segments | Retail Electricity | Non-trading
Less:
Net, gain (loss) on non-trading derivative instruments	8,047	(33,694)	(16,339)	(55,636)
Current period settlements on non-trading derivatives	9,367	12,669	24,332	20,842
Operating Segments | Retail Natural Gas
Segment Reporting Information [Line Items]
Total Revenues	16,363	17,029	60,955	75,091
Retail cost of revenues	6,337	10,572	24,777	39,940
Less:
Net asset optimization (expenses) revenues	0	0	0	0
Retail Gross Margin	9,421	8,110	34,076	34,713
Total Assets	882,142		882,142		820,601
Goodwill	2,530		2,530		2,530
Operating Segments | Retail Natural Gas | Non-trading
Less:
Net, gain (loss) on non-trading derivative instruments	(83)	(1,772)	(230)	367
Current period settlements on non-trading derivatives	688	119	2,332	71
Corporate and Other
Segment Reporting Information [Line Items]
Total Revenues	(82)	(56)	239	2,496
Retail cost of revenues	0	0	0	0
Less:
Net asset optimization (expenses) revenues	(82)	(56)	239	2,496
Retail Gross Margin	0	0	0	0
Total Assets	326,636		326,636		341,411
Goodwill	0		0		0
Corporate and Other | Non-trading
Less:
Net, gain (loss) on non-trading derivative instruments	0	0	0	0
Current period settlements on non-trading derivatives	0	0	0	0
Eliminations
Segment Reporting Information [Line Items]
Total Revenues	0	0	0	0
Retail cost of revenues	0	0	0	0
Less:
Net asset optimization (expenses) revenues	0	0	0	0
Retail Gross Margin	0	0	0	0
Total Assets	(3,569,084)		(3,569,084)		(3,263,928)
Goodwill	0		0		$ 0
Eliminations | Non-trading
Less:
Net, gain (loss) on non-trading derivative instruments	0	0	0	0
Current period settlements on non-trading derivatives	$ 0	$ 0	$ 0	$ 0