Annual report pursuant to Section 13 and 15(d)

Leases (Narrative) (Details)

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Leases (Narrative) (Details)
$ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Operating Leased Assets [Line Items]      
Number of real estate leases 34    
Number Of Service Center Locations 228    
Aggregate expense under operating leases $ 14.1 $ 13.8 $ 15.2