Share-Based Payments (Details 3) - Stock Option Stock Appreciation Rights - $ / shares	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Number of Options and SAR
Outstanding at the beginning of the period (in shares)	2,080,749	1,463,043	1,463,043
Granted (in shares)	950,800	672,185
Exercised (in shares)	(177,270)	(14,814)
Forfeited or expired (in shares)	(127,965)	(40,620)
Outstanding at the end of the period (in shares)	2,726,314	2,079,794	2,080,749	1,463,043
Vested and expected to vest (in shares)	2,672,876	2,032,896	2,041,026	1,425,752
Exercisable (in shares)	879,346	546,672	626,548	256,227
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 7.93	$ 7.27	$ 7.27
Granted (in dollars per share)	10.06	9.21
Exercised (in dollars per share)	4.19	2.95
Forfeited or expired (in dollars per share)	8.56	7.56
Outstanding at the end of the period (in dollars per share)	8.89	7.93	7.93	$ 7.27
Vested and expected to vest (in dollars per share)	8.87	7.91	7.91	7.26
Exercisable (in dollars per share)	$ 7.96	$ 6.55	$ 6.40	$ 4.47
Weighted-Average Remaining Contractual Term (in years)
Outstanding at the end of the period	8 years 1 month 21 days	8 years 3 months 11 days	8 years 15 days	8 years 6 months 4 days
Vested and expected to vest	8 years 1 month 17 days	8 years 3 months 7 days	8 years 11 days	8 years 6 months
Exercisable	7 years 1 month 17 days	7 years 2 months 5 days	6 years 10 months 28 days	6 years 5 months 9 days