Pension Benefits and Other Postretirement Benefit Plans (Additional Information) (Details) $ in Millions	3 Months Ended
Mar. 31, 2018 plan	Mar. 31, 2017 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of qualified noncontributory defined benefit plans \| plan	2
Bear Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Required employer contribution \| $		$ 0.1

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.

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