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Share-based Compensation - Summary of Additional Restricted Stock Information (Detail) - Restricted Stock [Member] - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted-average grant date fair value per share $ 19.42 $ 15.13 $ 15.36 $ 15.29
Fair value of restricted stock awards that vested     $ 2,198