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Stock-Based Compensation - Effect of Recording Stock-Based Compensation (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total stock-based compensation $ 13,013 $ 11,315 $ 13,992
Tax effect on stock-based compensation (836) (331) (495)
Net effect on net income $ 12,177 $ 10,984 $ 13,497
Basic $ 0.23 $ 0.21 $ 0.25
Diluted $ 0.23 $ 0.21 $ 0.25
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total stock-based compensation $ 11,885 $ 10,203 $ 12,982
Employee Stock Purchase Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total stock-based compensation $ 1,128 $ 1,112 $ 1,010