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Share-Based Compensation - Summary of Activity Related to Stock Options Granted under 2008 Plan (Detail)
$ / shares in Units, $ in Thousands
9 Months Ended
Sep. 30, 2017
USD ($)
$ / shares
shares
2008 Plan [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Total Shares outstanding, Beginning balance 1,272,000
Total Shares, Granted 0
Total Shares, Exercised (537,000)
Total Shares, Forfeited, canceled or expired (2,000)
Total Shares outstanding, Ending balance 733,000
Total Shares, Exercisable 733,000
Employee Stock Option [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Total Shares, Granted 0
Employee Stock Option [Member] | 2008 Plan [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Weighted Average Exercise Price per Share Outstanding, Beginning balance | $ / shares $ 15.26
Weighted Average Exercise Price per Share, Granted | $ / shares 0
Weighted Average Exercise Price per Share, Exercised | $ / shares 12.57
Weighted Average Exercise Price per Share, Forfeited, canceled or expired | $ / shares 16.35
Weighted Average Exercise Price per Share Outstanding, Ending balance | $ / shares 17.23
Weighted Average Exercise Price per Share, Exercisable | $ / shares $ 17.23
Weighted Average Remaining Contractual Term (Years), Outstanding 2 years 11 months 1 day
Weighted Average Remaining Contractual Term (Years), Exercisable 2 years 11 months 1 day
Aggregate Intrinsic Value, Outstanding | $ $ 53,939
Aggregate Intrinsic Value, Exercisable | $ $ 53,939