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Goodwill and Other Intangible Assets - Narrative (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Intangible asset balances by major asset class      
Goodwill $ 299.6 $ 306.5  
Amortization of intangible assets 3.0 $ 3.0 $ 3.3
Future amortization expense, 2017 2.0    
Future amortization expense, 2018 0.4    
Future amortization expense, 2019 0.4    
Future amortization expense, 2020 0.4    
Future amortization expense, 2021 $ 0.4    
Customer relationships      
Intangible asset balances by major asset class      
Finite-lived intangible asset, useful life 10 years