Idaho Public Utilities Commission (IPUC) (Details) - IPUC - Tax Cuts and Jobs Act - USD ($) $ in Millions	May 10, 2018	Mar. 23, 2018	Mar. 12, 2018
Public Utilities, General Disclosures [Line Items]
State corporate income tax rate			7.40%
State corporate income tax rate, current			6.90%
Public utilities, requested rate increase (decrease), amount		$ (5.0)
Public utilities, approved rate increase (decrease), amount	$ (5.1)
Public utilities, approved rate increase (decrease), percentage	(2.30%)