Postretirement Benefits Other than Pensions - Discount Rate to Determine the Net Postretirement Benefit Expense (Details) - Other Postretirement Benefit Plan [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (as a percent)	3.15%	3.47%	3.57%
Expected contribution to plan in 2019	$ 0.3

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration