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Shareholders' Equity - Summary of Activities in Common Stock (Detail) - USD ($)
shares in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Equity [Abstract]      
Stock option exercises, Shares 1,126 1,113 827
Purchases of common stock, Shares (781) (44) (882)
Employee stock plan purchases, Shares 45 51 47
Stock option exercises $ 74,907 $ 49,845 $ 23,527
Purchases of common stock, Amount (150,050) (6,613) (112,699)
Employee stock plan purchases, Amount $ 8,051 $ 7,044 $ 6,236