Stockholders' Equity - Activity Related to Stock Option Plans (Details)	6 Months Ended
	Jun. 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)	(1,095,065)
Options outstanding, number of shares granted (in shares)	1,095,065
Options outstanding, number of shares, exercised (in shares)	(2,208,741)
Options outstanding, number of shares expired (in shares)	(48)
Shares available for grant, ending balance (in shares)	22,516,496
Options outstanding, number of shares, ending balance (in shares)	19,745,602
Options vested and exercisable, number of shares, ending balance (in shares)	19,745,602
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	375.86
Options outstanding, weighted-average exercise price, exercised (dollars per share) | $ / shares	60.06
Options expired, weighted-average exercise price (dollars per share) | $ / shares	9.96
Options outstanding, weighted-average exercise price, ending balance (dollars per share) | $ / shares	145.42
Options outstanding, weighted-average exercise price, vested and exercisable (dollars per share) | $ / shares	$ 145.42