Share-Based Payments (Details 3) (Stock Option Stock Appreciation Rights, USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Stock Option Stock Appreciation Rights
Number of Options and SAR
Outstanding at the beginning of the period (in shares)	1,463,043
Granted (in shares)	672,185
Exercised (in shares)	(14,814)
Forfeited or expired (in shares)	(40,620)
Outstanding at the end of the period (in shares)	2,079,794	1,463,043
Vested and expected to vest (in shares)	2,032,896	1,425,752
Exercisable (in shares)	546,672	256,227
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 7.27
Granted (in dollars per share)	$ 9.21
Exercised (in dollars per share)	$ 2.95
Forfeited or expired (in dollars per share)	$ 7.56
Outstanding at the end of the period (in dollars per share)	$ 7.93	$ 7.27
Vested and expected to vest (in dollars per share)	$ 7.91	$ 7.26
Exercisable (in dollars per share)	$ 6.55	$ 4.47
Weighted-Average Remaining Contractual Term
Outstanding at the end of the period	8 years 3 months 11 days	8 years 6 months 4 days
Vested and expected to vest	8 years 3 months 7 days	8 years 6 months
Exercisable	7 years 2 months 5 days	6 years 5 months 9 days