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Stock-Based Compensation (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Stock-Based Compensation      
Stock-based compensation expense $ 5.6 $ 4.8 $ 4.0
Income tax benefit $ 2.1 $ 1.8 1.5
Stock Options      
Shares      
Outstanding at beginning of year (in shares) 910    
Granted (in shares) 132    
Exercised (in shares) (318)    
Outstanding at end of year (in shares) 724 910  
Options exercisable at end of year (in shares) 437    
Weighted-Average Exercise Price      
Outstanding at beginning of year (in dollars per share) $ 12.95    
Granted (in dollars per share) 19.67    
Exercised (in dollars per share) 11.78    
Outstanding at end of year (in dollars per share) $ 14.69 $ 12.95  
Other information      
Intrinsic value of options exercised $ 3.9 $ 0.4 $ 3.0
Weighted-average remaining contractual term of options exercisable 5 years 4 months 24 days    
Aggregate intrinsic value of options exercisable $ 6.8    
Number of options that are vested and expected to vest (in shares) 700    
Weighted average exercise price of options that are vested and expected to vest (in dollars per share) $ 14.69    
Weighted-average remaining contractual term of options that are vested and expected to vest 6 years 7 months 6 days    
Aggregate intrinsic value of options that are vested and expected to vest $ 9.9