Contingencies (Schedule of Changes in Claims) (Details) - Asbestos Litigation [Member] $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018 USD ($) claims	Dec. 31, 2017 USD ($) claims	Dec. 31, 2016 USD ($) claims	Dec. 31, 2015 USD ($) claims	Dec. 31, 2014 USD ($) claims	Dec. 31, 2013 USD ($) claims
Loss Contingencies [Line Items]
Opening Number of Claims	3,730	3,745	3,791	3,821	4,299	4,463
Claims Dismissed, Settled, or Resolved	105	105	148	116	625	230
New Claims	52	90	102	86	147	66
Closing Number of Claims	3,677	3,730	3,745	3,791	3,821	4,299
Amounts Paid (thousands) to Settle or Resolve | $	$ 93	$ 55	$ 758	$ 164	$ 437	$ 78