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Stockholders' Equity and Stock-Based Compensation - Summary of Activity Related to Employee Stock Purchase Plan (Detail) - ESPP [Member] - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares Issued 148 94 70
Weighted- Average Purchase Price $ 80.21 $ 38.83 $ 38.98
Total Cash Proceeds $ 11,863 $ 3,635 $ 2,721