Equity - Basic and Diluted Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Equity [Abstract]
Net (loss) income attributable to Spark Energy, Inc. stockholders	$ (7,631)	$ 4,479
Less: Dividends on Series A preferred stock	1,951	1,500
Net (loss) income attributable to stockholders of Class A common stock	$ (9,582)	$ 2,979
Basic weighted average Class A common shares outstanding (in shares)	14,627	14,381
Basic income (loss) per share attributable to stockholders (in dollars per share)	$ (0.66)	$ 0.21
Net (loss) income attributable to stockholders of Class A common stock	$ (9,582)	$ 2,979
Effect of conversion of Class B common stock to shares of Class A common stock	0	0
Diluted net (loss) income attributable to stockholders of Class A common stock	$ (9,582)	$ 2,979
Basic weighted average Class A common shares outstanding (in shares)	14,627	14,381
Effect of dilutive Class B common stock (in shares)	0	0
Effect of dilutive restricted stock units (in shares)	0	403
Diluted weighted average shares outstanding (in shares)	14,627	14,784
Diluted (loss) income per share attributable to stockholders (in dollars per share)	$ (0.66)	$ 0.20