Common Stock and Stockholders' Equity - Stock Plan and Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Stock options
Common Stock and Stockholders' Equity
Shares available for grant	8,161,962
Aggregate Intrinsic Value
Grant-date fair value of stock options granted during the period	$ 300	$ 1,200
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)	7,441
Stock option exercised (in shares)	(671,279)
Stock options forfeited (in shares)	(126,577)
Balance, end of period (in shares)	4,416,566		5,206,981
Vested or expected to vest at end of period (in shares)	4,414,765
Exercisable as of end of period (in shares)	3,055,075
Weighted-Average Exercise Price
Balance, beginning of period (in dollars per share)	$ 24.47
Stock option grants (in dollars per share)	106.25
Stock option exercised (in dollars per share)	22.10
Stock options forfeited (in dollars per share)	34.48
Balance, end of period (in dollars per share)	24.67		$ 24.47
Vested or expected to vest at end of period (in dollars per share)	24.67
Exercisable as of end of period (in dollars per share)	$ 19.80
Weighted-average remaining contractual life in Years
Weighted-average remaining contractual life (in years)	6 years 9 months 7 days		7 years 10 days
Vested or expected to vest at end of period (in years)	6 years 9 months 7 days
Exercisable as of end of period (in years)	6 years 4 months 28 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 575,408		$ 308,538
Stock options exercised	(65,192)
Vested or expected to vest at end of period	575,408
Exercisable as of end of period	$ 413,071