Basis of Presentation and Summary of Significant Accounting Policies - Immaterial Corrections to Prior Year Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Additional paid-in capital	$ 42,329	$ 46,715	$ 42,329	$ 46,715		$ 46,157
Retained earnings	(7,053)	219	(7,053)	219		1,307
Total Stockholders' Equity	33,581	45,241	33,581	45,241		45,806
Non-controlling interest in Spark HoldCo, LLC	18,124	63,327	18,124	63,327		44,488
Total equity	51,705	108,568	51,705	108,568	$ 85,750	$ 90,294	$ 108,754	$ 159,095
Net income attributable to stockholders of Class A common stock	(9,142)	6,758	(10,387)	(6,374)
Net income attributable to non-controlling interests	(18,369)	15,142	(16,406)	(15,584)
Net income attributable to Spark Energy, Inc. stockholders	$ (7,115)	$ 8,785	$ (6,333)	$ (2,320)
Net income attributable to Spark Energy, Inc. per share of Class A common stock
Basic (in dollars per share)	$ (0.64)	$ 0.51	$ (0.73)	$ (0.48)
Diluted (in dollars per share)	$ (0.73)	$ 0.51	$ (0.73)	$ (0.52)
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Additional paid-in capital		$ 28,846		$ 28,846
Retained earnings		(2,678)		(2,678)
Total Stockholders' Equity		24,475		24,475
Non-controlling interest in Spark HoldCo, LLC		86,302		86,302
Total equity		110,777		110,777
Net income attributable to stockholders of Class A common stock		5,473		(8,880)
Net income attributable to non-controlling interests		16,427		(13,078)
Net income attributable to Spark Energy, Inc. stockholders		$ 7,500		$ (4,826)
Net income attributable to Spark Energy, Inc. per share of Class A common stock
Basic (in dollars per share)		$ 0.41		$ (0.67)
Diluted (in dollars per share)		$ 0.41		$ (0.67)
Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Additional paid-in capital		$ 17,869		$ 17,869
Retained earnings		2,897		2,897
Total Stockholders' Equity		20,766		20,766
Non-controlling interest in Spark HoldCo, LLC		(22,975)		(22,975)
Total equity		(2,209)		(2,209)
Net income attributable to stockholders of Class A common stock		1,285		2,506
Net income attributable to non-controlling interests		(1,285)		(2,506)
Net income attributable to Spark Energy, Inc. stockholders		$ 1,285		$ 2,506
Net income attributable to Spark Energy, Inc. per share of Class A common stock
Basic (in dollars per share)		$ 0.10		$ 0.19
Diluted (in dollars per share)		$ 0.10		$ 0.15