Employee Benefits Supplemental Executive Retirement Plans and Long Term Incentive Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred Compensation Arrangement with Individual, Compensation Expense	$ 0.9	$ 0.6	$ (0.1)
Holding Company SERP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation	7.9	8.2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 0.4	$ 0.5	$ 0.5
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.60%	4.10%	4.35%
Pacific Northwest SERP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation	$ 3.2	$ 3.2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		$ 0.2	$ 0.2
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.37%	3.62%	3.81%
KLS LTIP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation	$ 8.1	$ 7.6
Deferred Compensation Arrangement with Individual, Compensation Expense	$ 0.5	$ (0.2)	$ 1.3
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.33%	3.70%	3.90%