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Stockholders' Equity - Schedule of Options Exercisable, Vested or Expected to Vest (Details) - $ / shares
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Equity [Abstract]      
Options exercisable at end of year 10,237,202 7,436,379 6,523,093
Options vested or expected to vest 18,179,553 15,962,432 14,449,017
Options exercisable at end of year, weighted average exercise price $ 18.74 $ 17.02 $ 14.83
Options vested or expected to vest, weighted average exercise price $ 19.58 $ 20.31 $ 18.11