Stockholders' Equity - Activity Related to Stock Option Plans (Details)	9 Months Ended
	Sep. 30, 2020 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares available for grant, beginning balance (in shares)	6,111,561
Options outstanding, number of shares, beginning balance (in shares)	20,859,326
Shares available for grant, number of shares authorized (in shares)	17,500,000
Options outstanding, number of shares granted (in shares)	(1,498,232)
Options outstanding, number of shares granted (in shares)	1,498,232
Options outstanding, number of shares, exercised (in shares)	(2,988,359)
Options outstanding, number of shares expired (in shares)	(188)
Shares available for grant, ending balance (in shares)	22,113,329
Options outstanding, number of shares, ending balance (in shares)	19,369,011
Options vested and exercisable, number of shares, ending balance (in shares)	19,369,011
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Options outstanding, weighted-average exercise price, beginning balance (dollars per share) | $ / shares	$ 124.28
Options outstanding, weighted-average exercise price, granted (dollars per share) | $ / shares	412.45
Options outstanding, weighted-average exercise price, exercised (dollars per share) | $ / shares	67.58
Options expired, weighted-average exercise price (dollars per share) | $ / shares	13.38
Options outstanding, weighted-average exercise price, ending balance (dollars per share) | $ / shares	155.32
Options outstanding, weighted-average exercise price, vested and exercisable (dollars per share) | $ / shares	$ 155.32