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Earnings Per Share - Summary of Earnings Per Share (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Numerator (in millions):      
Net income available to common stockholders $ 81.3 $ 119.5 $ 84.1
Denominator (in thousands):      
Weighted average common shares outstanding 23,998 24,107 24,391
Dilutive effect of stock options and awards 444 505 487
Denominator for diluted earnings per share 24,442 24,612 24,878
Net income per share, basic: $ 3.39 $ 4.96 $ 3.45
Net income per share, diluted: $ 3.33 $ 4.86 $ 3.38