Acquisitions (Details) rce in Thousands				3 Months Ended		6 Months Ended
	Mar. 01, 2018 USD ($) market rce state	Jul. 01, 2017 USD ($)	Apr. 01, 2017 USD ($) utility	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jan. 12, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Revenues				$ 232,251,000	$ 151,436,000	$ 518,939,000	$ 347,743,000
Net income from operations				28,941,000	$ 7,797,000	(17,313,000)	$ 24,580,000
Debt outstanding				125,921,000		125,921,000			$ 145,744,000
Verde Earnout Termination Note | Promissory Note
Business Acquisition [Line Items]
Debt outstanding								$ 5,900,000
HIKO Energy, LLC
Business Acquisition [Line Items]
Purchase price	$ 6,000,000
Number of RCEs | rce	29
Number of markets | market	42
Number of states | state	7
Initial positive (negative) working capital estimate						700,000
Revenues				5,200,000		8,000,000
Net income from operations				$ 1,600,000		2,700,000
Verde Companies
Business Acquisition [Line Items]
Purchase price		$ 90,700,000
Initial positive (negative) working capital estimate		20,100,000				$ 500,000
Consideration transferred, amount funded		85,800,000
Consideration transferred, cash on hand		6,800,000
Consideration transferred, liabilities incurred		$ 5,400,000
Adjusted EBITDA obligation, percent		100.00%
Adjusted EBITDA obligation term (in months)		18 months
Earnout period (in months)		18 months
Verde Companies | Trademarks
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life (in years)						5 years
Verde Companies | Promissory Note
Business Acquisition [Line Items]
Consideration transferred, liabilities incurred		$ 20,000,000.0
Verde Companies | Revolving Credit Facility
Business Acquisition [Line Items]
Consideration transferred, liabilities incurred		44,000,000
Verde Companies | Subordinated debt — affiliate
Business Acquisition [Line Items]
Consideration transferred, liabilities incurred		$ 15,000,000
Perigee Energy, LLC | National Gas & Electric, LLC
Business Acquisition [Line Items]
Purchase price			$ 4,100,000
Initial positive (negative) working capital estimate			$ 1,900,000
Number of utilities | utility			14
Base price			$ 2,000,000
Additional customer option payment			$ 200,000