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Stock-Based Compensation - Restricted Stock Units Unvested Roll Forward (Detail) - Restricted Stock Units (RSUs) [Member]
shares in Thousands
12 Months Ended
Dec. 31, 2020
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]  
Unvested Beginning balance, Shares | shares 260
Shares, Granted | shares 119
Shares, Vested | shares (88)
Shares, Forfeited | shares (20)
Unvested Ending balance, Shares | shares 271
Weighted-average grant date fair value per share of shares unvested at beginning of period | $ / shares $ 184.70
Weighted-average grant date fair value per share of shares granted | $ / shares 206.99
Weighted-average grant date fair value per share of shares vested | $ / shares 162.43
Weighted-average grant date fair value of shares forfeited | $ / shares 180.90
Weighted-average grant date fair value per share of shares unvested at end of period | $ / shares $ 202.00