REGULATORY MATTERS: Idaho Fixed Cost Adjustment (Details) - Idaho Fixed Cost Adjustment - USD ($) $ in Millions	Jun. 01, 2014	Jun. 01, 2013	Jun. 01, 2012
Idaho Fixed Cost Adjustment [Line Items]
Percentage cap on the FCA adjustment	3.00%
Annual fixed cost adjustment mechanism deferral	$ 16.9	$ 14.9	$ 8.9