Equity - Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands					12 Months Ended
		Jan. 31, 2017	Jan. 08, 2017	Oct. 05, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Spark Energy, Inc. stockholders					$ 18,854	[1]	$ 14,444	[2]	$ 3,865	[3]
Less: Dividend on Series A preferred stock	[1]				3,038		0	[2]	0	[3]
Net income attributable to stockholders of Class A common stock					$ 15,816	[1]	$ 14,444	[2]	$ 3,865	[3]
Basic weighted average Class A common shares outstanding (in shares)					13,143,000	[1]	11,402,000	[2]	6,129,000	[3]
Basic EPS attributable to stockholders (in dollars per share)					$ 1.20	[1]	$ 1.27	[2]	$ 0.63	[3]
Effect of conversion of Class B common stock to shares of Class A common stock					$ 0		$ 0		$ 0
Effect of conversion of convertible subordinated notes into shares of Class B common stock and shares of Class B common stock into shares of Class A common stock					0		(310)		(334)
Diluted net income attributable to stockholders of Class A common stock					$ 15,816		$ 14,134		$ 3,531
Basic weighted average Class A common shares outstanding (in shares)					13,143,000	[1]	11,402,000	[2]	6,129,000	[3]
Effect of dilutive Class B common stock (in shares)					0		0		0
Effect of conversion of convertible subordinated notes into shares of Class B common stock and shares of Class B common stock into shares of Class A common stock (in shares)					0		1,010,000		420,000
Effect of dilutive restricted stock units (in shares)					203,000		278,000		106,000
Diluted weighted average shares outstanding (in shares)					13,346,000	[1]	12,690,000	[2]	6,655,000	[3]
Diluted EPS attributable to stockholders (in dollars per share)					$ 1.19	[1]	$ 1.11	[2]	$ 0.53	[3]
CenStar Note | Common Class B
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Number of shares, irrevocable commitment to convert (in shares)			269,462	269,462
Oasis Note | Common Class B
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Number of shares, irrevocable commitment to convert (in shares)		766,180		766,180

[1] Financial information includes results attributable to the acquisition of Perigee Energy, LLC by an affiliate on February 3, 2017. See Notes 2 and 3 "Basis of Presentation and Summary of Significant Accounting Policies" and "Acquisitions," respectively, for further discussion.

[2] Financial information includes results attributable to the acquisition of Major Energy Companies from an affiliate on April 15, 2016. See Notes 2 and 3 "Basis of Presentation and Summary of Significant Accounting Policies" and "Acquisitions," respectively, for further discussion.

[3] Financial information includes results attributable to the acquisition of Oasis Power Holdings LLC from an affiliate on May 12, 2015. See Notes 2 and 3 "Basis of Presentation and Summary of Significant Accounting Policies" and "Acquisitions," respectively, for further discussion.