Share-Based Payments - Activity (Details) - Stock option and Stock Appreciation Rights - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Number of Options and SAR
Outstanding at the beginning of the period (in shares)	3,644,088
Granted (in shares)	1,063,255
Exercised (in shares)	(152,453)
Forfeited or expired (in shares)	(45,286)
Outstanding at the end of the period (in shares)	4,509,604	3,644,088
Vested and expected to vest (in shares)	4,509,604	3,591,528
Exercisable (in shares)	2,164,607	1,503,004
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 10.25
Granted (in dollars per share)	25.71
Exercised (in dollars per share)	8.24
Forfeited or expired (in dollars per share)	16.84
Outstanding at the end of the period (in dollars per share)	13.89	$ 10.25
Vested and expected to vest (in dollars per share)	13.89	10.22
Exercisable (in dollars per share)	$ 9.31	$ 8.62
Weighted-Average Remaining Contractual Term (in years)
Outstanding at the end of the period	7 years 8 months 16 days	7 years 7 months 2 days
Vested and expected to vest	7 years 8 months 16 days	7 years 6 months 26 days
Exercisable	6 years 6 months 4 days	6 years 5 months 27 days