Earnings per Share (Details) (USD $)
In Millions, except Share data, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Numerator:    
Net earnings $ 60.6 $ 50.2
Less: net earnings allocated to participating securities (0.3) [1] (0.4) [1]
Net earnings available to common shareholders $ 60.3 $ 49.8
Denominator:    
Weighted-average common shares outstanding, shares for basic earnings per share (in shares) 33,626,000 33,502,000
Weighted-average awards outstanding (in shares) 23,000 [2] 18,000 [2]
Shares for diluted earnings per share (in shares) 33,649,000 33,520,000
Net earnings per common share, basic (in dollars per share) $ 1.79 $ 1.49
Net earnings per common share, diluted (in dollars per share) $ 1.79 $ 1.49
Participating securities (in shares) 216,000 220,000
Weighted anti-dilutive awards outstanding (in shares) 343,000 373,000
[1] Participating securities include options, PSUs and RSUs that receive non-forfeitable dividends. Net earnings were allocated to participating securities of 216,000 and 220,000 for the three months ended March 31, 2015 and 2014, respectively.
[2] For the calculation of diluted earnings per share, the Company uses the more dilutive of either the treasury stock method or the two-class method, to determine the weighted average number of outstanding common shares. In addition, the Company had 343,000 and 373,000 weighted-awards outstanding for the three months ended March 31, 2015 and 2014, respectively, which were anti-dilutive and therefore not included in the diluted earnings per-share calculation.