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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, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]        
Weighted average grant-date fair value per share of options granted $ 12.07 $ 12.33 $ 11.51 $ 12.33
Total intrinsic value of options exercised $ 1,892 $ 1,301 $ 2,129 $ 2,046
Cash received from options exercised 1,109 776 1,353 1,642
Tax benefit realized from options exercised $ 731 $ 503 $ 823 $ 791