Equity Earnings per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	7 Months Ended	12 Months Ended
	Jul. 31, 2014	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income (loss) attributable to Spark Energy, Inc. stockholders	$ (21)	$ (54)		$ 31,412	$ 26,093
Basic weighted average Class A common shares outstanding (1)		3,000
Basic EPS attributable to Spark Energy, Inc. stockholders (in dollars per share)		$ (0.02)
Effect of conversion of Class B common stock to shares of Class A common stock		0
Diluted net loss attributable to Spark Energy, Inc. stockholders		$ (54)
Effect of dilutive restricted stock units		0
Diluted weighted average shares outstanding		3,000
Diluted EPS attributable to Spark Energy, Inc. stockholders (in dollars per share)		$ (0.02)
Common Class A
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic weighted average Class A common shares outstanding (1)		3,000	[1]
Common Class B
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Effect of dilutive Class B common stock (1)		0	[1]

[1] Based on outstanding shares for the period from the Offering date of August 1, 2014 to December 31, 2014.