Share-Based Payments - (Table summarizes stock option and SAR activity) (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Number of Options
Outstanding at the beginning of the period (in shares)	569,911
Granted (in shares)	951,082
Exercised (in shares)	(45,387)
Forfeited or expired (in shares)	(17,218)
Outstanding at the end of the period (in shares)	1,458,388	569,911
Vested and expected to vest (in shares)	1,414,392	564,083
Exercisable (in shares)	194,322	200,312
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 5.72
Granted (in dollars per share)	$ 7.81
Exercised (in dollars per share)	$ 0.83
Forfeited or expired (in dollars per share)	$ 7.00
Outstanding at the end of the period (in dollars per share)	$ 7.23	$ 5.72
Vested and expected to vest (in dollars per share)	$ 7.20	$ 5.72
Exercisable (in dollars per share)	$ 3.93	$ 2.11
Weighted-Average Remaining Contractual Term
Outstanding at the beginning of the period	8 years 8 months 12 days	7 years 10 months 17 days
Vested and expected to vest	8 years 8 months 9 days	7 years 10 months 13 days
Exercisable	6 years 1 month 2 days	5 years 8 months 23 days
Outstanding at the end of the period	8 years 8 months 12 days	7 years 10 months 17 days