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Accounting for Derivative Instruments - Volumetric Underlying Derivative Transactions (Details) MWh in Thousands, MMBTU in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017 MWh MMBTU	Dec. 31, 2016 MWh MMBTU
Non-trading | Natural Gas | Buy
Derivatives, Fair Value [Line Items]
Net notional volume	9,136	8,016
Non-trading | Natural Gas Basis | Buy
Derivatives, Fair Value [Line Items]
Net notional volume	0	0
Non-trading | Electricity | Buy
Derivatives, Fair Value [Line Items]
Net notional volume | MWh	4,276	3,958
Trading | Natural Gas | Buy
Derivatives, Fair Value [Line Items]
Net notional volume	108
Trading | Natural Gas | Sell
Derivatives, Fair Value [Line Items]
Net notional volume		953
Trading | Natural Gas Basis | Buy
Derivatives, Fair Value [Line Items]
Net notional volume	0
Trading | Natural Gas Basis | Sell
Derivatives, Fair Value [Line Items]
Net notional volume		380

X

- Definition

Nominal energy measure used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure
Namespace Prefix:	us-gaap_
Data Type:	num:energyItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativesFairValueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_TradingActivityByTypeAxis=spke_NontradingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_NaturalGasReservesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PositionAxis=us-gaap_LongMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=spke_NaturalGasBasisMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=spke_ElectricityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_TradingActivityByTypeAxis=spke_DesignatedasTradingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PositionAxis=us-gaap_ShortMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: