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Commitments and Contingencies Asbestos Claimant and Settlement (Details) - Asbestos [Member]
 3 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
claimants
Dec. 31, 2017
USD ($)
claimants
Dec. 31, 2016
claimants
Loss Contingencies [Line Items]      
Loss Contingency, Pending Claims, Number 4,913 5,256 5,339
Loss Contingency, New Claims Filed, Number 50 173  
Loss Contingency, Claims Dismissed, Number 389 231  
Loss Contingency, Claims Settled, Number 4 25  
Average settlement amount per claim during period | $ $ 14,750 $ 8,930  
Total defense costs during period | $ $ 550,000 $ 2,280,000