Long-Term Deposit (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Storey County
Costs Incurred, Development of Property, Plant And Equipment, In Long-Term Deposits [Line Items]
Costs incurred related to projects that have been classified as long-term deposits	$ 2.6	$ 2.2
NV Energy
Costs Incurred, Development of Property, Plant And Equipment, In Long-Term Deposits [Line Items]
Costs incurred related to projects that have been classified as long-term deposits	$ 0.0	$ 1.1