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Stock-Based Compensation - Options Granted and Options Exercised Under Stock Option Plan (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]        
Weighted average grant-date fair value per share of options granted $ 16.49 $ 11.63 $ 14.93 $ 11.21
Total intrinsic value of options exercised $ 766 $ 1,493 $ 4,593 $ 7,138
Cash received from options exercised 413 856 2,057 4,113
Tax benefit realized from options exercised $ 195 $ 578 $ 1,170 $ 2,761