Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation Plans - Changes in Company's Common Stock Price During Reporting Period (Detail)

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Stock-Based Compensation Plans - Changes in Company's Common Stock Price During Reporting Period (Detail) - Stock Based Compensation Expense [Member] - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Common stock price at beginning of period $ 46.14 $ 25.51 $ 33.25 $ 14.90
Common stock price at end of period 45.99 30.26 45.99 30.26
(Decrease) increase in stock price $ (0.15) $ 4.75 $ 12.74 $ 15.36