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Stock-Based Compensation - Summary of Restricted Stock Unit Activity (Detail) - RSUs - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Restricted stock units outstanding, beginning balance (in shares) 1,312,725 1,226,787 1,303,891
Restricted stock units granted (in shares) 695,383 779,478 704,249
Restricted stock units released, vested (in shares) (606,250) (549,259) (593,528)
Special distribution shares released (in shares) (722) (1,781) (13,880)
Restricted stock units canceled (in shares) (63,502) (142,477) (173,460)
Special distribution shares canceled (in shares)   (23) (485)
Restricted stock units outstanding, ending balance (in shares) 1,337,634 1,312,725 1,226,787
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]      
Restricted stock units outstanding, weighted-average grant date fair value, beginning balance (in dollars per share) $ 411.99 $ 361.22 $ 252.30
Restricted stock units granted, weighted-average grant date fair value (in dollars per share) 596.80 448.16 387.31
Restricted stock units released, vested, weighted-average grant date fair value (in dollars per share) 426.03 362.66 299.07
Special distribution shares released, weighted-average grant date fair value (in dollars per share) 264.57 295.31 283.14
Restricted stock units canceled, weighted-average grant date fair value (in dollars per share) 457.91 364.42 336.75
Special distribution shares canceled, weighted-average grant date fair value (in dollars per share)   297.04 295.77
Restricted stock units outstanding, weighted-average grant date fair value, ending balance (in dollars per share) $ 499.60 $ 411.99 $ 361.22
Restricted stock units outstanding, weighted-average remaining contractual life (years) 1 year 2 months 19 days    
Restricted stock units outstanding, aggregate intrinsic value $ 955,311