Equity - Computation of Basic and Diluted Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Equity [Abstract]
Net income attributable to Spark Energy, Inc. stockholders	$ 15,534	$ 6,767	$ 9,201	$ 4,447
Less: Dividend on Series A preferred stock	2,026	2,027	6,080	6,081
Net income (loss) attributable to stockholders of Class A common stock	$ 13,508	$ 4,740	$ 3,121	$ (1,634)
Basic weighted average Class A common shares outstanding (in shares)	14,380	13,394	14,254	13,254
Basic income (loss) per share attributable to stockholders (in dollars per share)	$ 0.94	$ 0.35	$ 0.22	$ (0.12)
Net income (loss) attributable to stockholders of Class A common stock	$ 13,508	$ 4,740	$ 3,121	$ (1,634)
Effect of conversion of Class B common stock to shares of Class A common stock	0	0	0	0
Diluted net income (loss) attributable to stockholders of Class A common stock	$ 13,508	$ 4,740	$ 3,121	$ (1,634)
Basic weighted average Class A common shares outstanding (in shares)	14,380	13,394	14,254	13,254
Effect of dilutive Class B common stock (in shares)	0	0	0	0
Effect of dilutive restricted stock units (in shares)	134	0	175	0
Diluted weighted average shares outstanding (in shares)	14,514	13,394	14,429	13,254
Diluted income (loss) per share attributable to stockholders (in dollars per share)	$ 0.93	$ 0.35	$ 0.22	$ (0.12)