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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 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 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 $ 14.12 $ 10.96 $ 13.98 $ 10.96
Total intrinsic value of options exercised $ 967 $ 1,032 $ 3,827 $ 5,645
Cash received from options exercised 411 647 1,644 3,257
Tax benefit realized from options exercised $ 246 $ 399 $ 975 $ 2,183