Pension and Other Postretirement Benefit Plans (Contributory employee savings plan) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Domestic Plan
Defined Contribution Plan Disclosure [Line Items]
Matching contribution, contributory employee savings plan, amount	$ 0.5	$ 0.5	$ 0.6

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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