Share-Based Payments - Activity (Details) - Stock option and Stock Appreciation Rights - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Number of Options
Outstanding at the beginning of the period (in shares)	4,606,559
Granted (in shares)	1,126,525
Exercised (in shares)	(42,086)
Forfeited (in shares)	(41,800)
Outstanding at the end of the period (in shares)	5,649,198	4,606,559
Vested and expected to vest (in shares)	5,649,198	4,606,559
Exercisable (in shares)	3,354,282	2,598,112
Weighted- Average Exercise Price (per share)
Outstanding at the beginning of the period (in dollars per share)	$ 23.05
Granted (in dollars per share)	23.98
Exercised (in dollars per share)	11.58
Forfeited (in dollars per share)	26.66
Outstanding at the end of the period (in dollars per share)	23.30	$ 23.05
Vested and expected to vest (in dollars per share)	23.30	23.05
Exercisable (in dollars per share)	$ 18.85	$ 15.68
Weighted- Average Remaining Contractual Term (in years)
Outstanding at the end of the period	6 years 10 months 9 days	6 years 7 months 28 days
Vested and expected to vest	6 years 10 months 9 days	6 years 7 months 28 days
Exercisable	5 years 6 months 10 days	5 years 5 months 23 days