Pension and Other Postretirement Benefit Plans Deferred Compensation Arrangements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension and Other Postretirement Benefit Plans [Abstract]
Deferred Compensation Plan with Individual, Base Salary Period Used to Determine Benefit	5 years
Deferred Compensation Arrangement with Individual, Compensation Expense	$ 1.4	$ 1.2	$ 1.7
Deferred Compensation Arrangement with Individual, Employer Contribution	$ 0.1	$ 0.2	$ 0.3