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Schedule of Weighted Average Stock Options Exercise Price (Detail) - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award      
Outstanding at January 1 $ 7.89 $ 6.29 $ 4.64
Options granted 18.10 19.16 16.56
Options exercised 5.49 5.34 3.28
Options forfeited 8.67 3.59 2.57
Options cancelled 3.28 2.21 8.05
Outstanding at December 31 10.21 7.89 6.29
Exercisable at December 31 $ 6.92 $ 5.00 $ 4.55