Employee Benefit Plans - Stock Option Activity and Related Activity (Details) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares
Number of Shares
Balance as of beginning of period (in shares) | shares	0.1
Assumed upon the acquisition of Mist (in shares) | shares	1.1
Exercised (in shares) | shares	(0.1)
Expired/Canceled (in shares) | shares	(0.1)
Balance as of end of period (in shares) | shares	1.0
Weighted Average Exercise Price per Share
Balance as of beginning of period (in dollars per share) | $ / shares	$ 20.66
Assumed upon the acquisition of Mist (in dollars per share) | $ / shares	5.05
Exercised (in dollars per share) | $ / shares	16.45
Expired/Canceled (in dollars per share) | $ / shares	6.55
Balance as of end of period (in dollars per share) | $ / shares	$ 4.95
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, weighted average remaining contractual term	8 years 2 months 12 days
Outstanding, aggregate intrinsic value | $	$ 19.6
Exercisable options (in shares) | shares	0.2
Exercisable options, weighted average exercise price per share (in dollars per share) | $ / shares	$ 4.09
Exercisable options, weighted average remaining contractual term	7 years 8 months 12 days
Exercisable options, aggregate intrinsic value | $	$ 3.5
Vested and expected-to-vest options
Vested and expected-to-vest options (in shares) | shares	1.0
Vested and expected-to-vest options, weighted average exercise price per share (in dollars per share) | $ / shares	$ 4.95
Vested and expected-to-vest options, weighted average remaining contractual term	8 years 2 months 12 days
Vested and expected-to-vest option, aggregate intrinsic value | $	$ 19.6