Equity - Computation of Basic and Diluted Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity [Abstract]
Net (loss) income attributable to Spark Energy, Inc. stockholders	$ (7,115)	$ 8,785	$ (6,333)	$ (2,320)
Less: Dividend on Series A preferred stock	2,027	2,027	4,054	4,054
Net (loss) income attributable to stockholders of Class A common stock	$ (9,142)	$ 6,758	$ (10,387)	$ (6,374)
Basic weighted average Class A common shares outstanding (in shares)	14,246	13,229	14,191	13,183
Basic (loss) income per share attributable to stockholders (in dollars per share)	$ (0.64)	$ 0.51	$ (0.73)	$ (0.48)
Net (loss) income attributable to stockholders of Class A common stock	$ (9,142)	$ 6,758	$ (10,387)	$ (6,374)
Effect of conversion of Class B common stock to shares of Class A common stock	(16,557)	0	(15,242)	(11,601)
Diluted net (loss) income attributable to stockholders of Class A common stock	$ (25,699)	$ 6,758	$ (25,629)	$ (17,975)
Basic weighted average Class A common shares outstanding (in shares)	14,246	13,229	14,191	13,183
Effect of dilutive Class B common stock (in shares)	20,800	0	20,800	21,485
Effect of dilutive restricted stock units (in shares)	0	17	0	0
Diluted weighted average shares outstanding (in shares)	35,046	13,246	34,991	34,668
Diluted (loss) income per share attributable to stockholders (in dollars per share)	$ (0.73)	$ 0.51	$ (0.73)	$ (0.52)