Stockholders' Equity - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2018	Mar. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, beginning balance (in shares)	11,269
Granted (in shares)	0
Exercised (in shares)	(1,107)
Cancelled/forfeited (in shares)	(61)
Options outstanding, ending balance (in shares)	10,101
Options vested and exercisable (in shares)			6,443
Stock Options Weighted Average Exercise Price
Options outstanding, weighted average exercise price, beginning of period (in USD per share)	$ 4.89		$ 4.89	$ 4.68
Granted, weighted average exercise price (in USD per share)	0
Exercised, weighted average exercise price (in USD per share)	2.68
Cancelled/forfeited, weighted average exercise price (in USD per share)	6.94
Options outstanding, weighted average exercise price, end of period (in USD per share)	$ 4.89
Vested and exercisable, weighted-average exercise price (in USD per share)			$ 3.00
Stock Option Activity, Additional Disclosures
Weighted-average remaining contractual period	7 years 2 months 12 days	7 years 3 months 18 days
Aggregate intrinsic value			$ 142,692	$ 173,471
Vested and exercisable, weighted average contractual term	6 years 4 months 24 days
Vested and exercisable, aggregate intrinsic value			$ 102,947