Commitments and Contingencies (Details) $ in Thousands, portfolio_energy_credit in Millions		1 Months Ended						12 Months Ended
	Oct. 08, 2017	Sep. 30, 2018 USD ($) MWh	Jan. 31, 2018 MWh	Mar. 31, 2017	Sep. 30, 2016 USD ($)	Nov. 30, 2015 portfolio_energy_credit	Jun. 30, 2015	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2018 USD ($) MWh	Feb. 01, 2018 USD ($)
Long-term Purchase Commitment [Line Items]
Purchase commitment											$ 33,400
Unrecorded Unconditional Purchase Obligation, Due within Three Years								$ 900
Regulatory fee expense								0	$ 649	$ 27,018
Self Insurance Reserve								500	400
Portfolio Energy Credits [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months								1,907
Purchase commitment								33,134
Future power purchase commitments for 2019								1,907
Unrecorded Unconditional Purchase Obligation, Due within Three Years								1,739
Unrecorded Unconditional Purchase Obligation, Due within Four Years								1,739
Unrecorded Unconditional Purchase Obligation, Due within Five Years								1,738
Unrecorded Unconditional Purchase Obligation, Due after Five Years								24,104
Energy
Long-term Purchase Commitment [Line Items]
Number of megawatts per hour required under purchase commitment | MWh											40
Term of purchase commitment				36 months
Fiber Transport Services [Member]
Long-term Purchase Commitment [Line Items]
Term of purchase commitment					24 months
Purchase commitment								1,800
Future power purchase commitments for 2019								900
Unrecorded Unconditional Purchase Obligation, Monthly					$ 100
Tenaska Power Services Co. [Member]
Long-term Purchase Commitment [Line Items]
Purchase commitment		$ 6,500
Tenaska Power Services Co. [Member] | Energy
Long-term Purchase Commitment [Line Items]
Number of megawatts per hour required under purchase commitment | MWh		10	10
Term of purchase commitment		6 years	23 months
Purchase commitment		$ 1,200										$ 4,900
Future power purchase commitments for 2019								3,400
Tenaska Power Services Co. [Member] | Scheduling Services
Long-term Purchase Commitment [Line Items]
Purchase commitment		$ 400
Morgan Stanley Capital Group [Member] | Energy
Long-term Purchase Commitment [Line Items]
Purchase commitment									15,800
Future power purchase commitments for 2019									11,100
Unrecorded Unconditional Purchase Obligation, Due within Three Years									$ 4,700
Portfolio Energy Credits [Member] | Switch Station 1 [Member]
Long-term Purchase Commitment [Line Items]
Term of purchase commitment							20 years
Purchase commitment								20,300
Portfolio Energy Credits [Member] | Southern Nevada Water Authority [Member]
Long-term Purchase Commitment [Line Items]
Number of megawatts per hour required under purchase commitment | portfolio_energy_credit						82
Term of purchase commitment						5 years
Purchase commitment								300
Portfolio Energy Credits [Member] | Switch Station 2 [Member]
Long-term Purchase Commitment [Line Items]
Term of purchase commitment	20 years
Purchase commitment								$ 12,500