Common Stock and Stockholders' Equity - Stock Plan and Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Stock options
Common Stock and Stockholders' Equity
Shares available for grant	8,179,285		8,179,285
Stock options | Maximum
Common Stock and Stockholders' Equity
Exercisable period (in years)			10 years
2015 Incentive Award Plan
Number of Shares Outstanding
Balance, beginning of period (in shares)			5,206,981
Stock option grants (in shares)			10,832
Stock option exercised (in shares)			(1,598,963)
Stock options forfeited (in shares)			(148,655)
Balance, end of period (in shares)	3,470,195		3,470,195		5,206,981
Vested or expected to vest at end of period (in shares)	3,470,194		3,470,194
Exercisable as of end of period (in shares)	2,439,319		2,439,319
Weighted-Average Exercise Price
Balance, beginning of period (in dollars per share)			$ 24.47
Stock option grants (in dollars per share)			125.65
Stock option exercised (in dollars per share)			21.00
Stock options forfeited (in dollars per share)			32.82
Balance, end of period (in dollars per share)	$ 25.97		25.97		$ 24.47
Vested or expected to vest at end of period (in dollars per share)	25.97		25.97
Exercisable as of end of period (in dollars per share)	$ 20.94		$ 20.94
Weighted-average remaining contractual life in Years
Weighted-average remaining contractual life (in years)			6 years 7 months 13 days		7 years 10 days
Vested or expected to vest at end of period (in years)			6 years 7 months 13 days
Exercisable as of end of period (in years)			6 years 3 months 10 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 575,590		$ 575,590		$ 308,538
Vested or expected to vest at end of period	575,590		575,590
Exercisable as of end of period	414,445		414,445
Grant-date fair value of stock options granted during the period	$ 200	$ 1,200	$ 500	$ 2,400