Share-Based Payments (Details 3) (Stock option, USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assumptions used in estimating the fair value of each option award using the Black-Scholes option-pricing model
Expected volatility, minimum (as a percent)	69.50%	68.30%	59.10%
Expected volatility, maximum (as a percent)	70.90%	71.60%	74.70%
Dividend Yield (as a percent)	0.00%	0.00%	0.00%
Expected term		6 years 3 months
Risk-free rate, minimum (as a percent)	1.20%	0.89%	0.15%
Risk-free rate, maximum (as a percent)	2.94%	1.14%	2.93%
Expected forfeiture rate (as a percent)	5.00%
Number of Options
Outstanding at the beginning of the period (in shares)	569,911	598,109
Granted (in shares)	974,582	188,136
Exercised (in shares)	(62,513)	(159,264)
Forfeited or expired (in shares)	(18,937)	(57,070)
Outstanding at the end of the period (in shares)	1,463,043	569,911	598,109
Vested and expected to vest (in shares)	1,425,752
Exercisable (in shares)	256,227
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 5.72	$ 2.75
Granted (in dollars per share)	$ 7.79	$ 10.73
Exercised (in dollars per share)	$ 1.25	$ 1.67
Forfeited or expired (in dollars per share)	$ 6.47	$ 2.45
Outstanding at the end of the period (in dollars per share)	$ 7.27	$ 5.72	$ 2.75
Vested and expected to vest (in dollars per share)	$ 7.26
Exercisable (in dollars per share)	$ 4.47
Weighted-Average Remaining Contractual Term
Outstanding at the end of the period	8 years 6 months 4 days	7 years 10 months 17 days	7 years 8 months 16 days
Vested and expected to vest	8 years 6 months
Exercisable	6 years 5 months 8 days
Share-based payments, additional disclosure
Aggregate intrinsic value of options outstanding	$ 1,400,000	$ 1,600,000	$ 1,900,000
Aggregate intrinsic value of options vested and expected to vest	1,400,000	1,500,000	1,800,000
Aggregate intrinsic value of options exercisable	1,000,000	1,000,000	1,200,000
Weighted-average, grant-date fair value of options granted (in dollars per share)	$ 4.98	$ 6.85	$ 3.64
Total fair value of the common stock vested	512,000	218,000	113,000
Total intrinsic value of options exercised	377,000	748,000	262,000
Total unrecognized compensation expense, net of related forfeiture estimates	$ 4,611,000	$ 1,651,000
Weighted-average period over which total unrecognized compensation expense is expected to be recognized	2 years 11 months 8 days	3 years 22 days
Minimum
Assumptions used in estimating the fair value of each option award using the Black-Scholes option-pricing model
Fair value of common stock (in dollars per share)	$ 5.40	$ 5.07	$ 2.56
Expected term	6 years 3 months		4 months 28 days
Expected forfeiture rate (as a percent)		0.00%	0.00%
Maximum
Assumptions used in estimating the fair value of each option award using the Black-Scholes option-pricing model
Fair value of common stock (in dollars per share)	$ 7.90	$ 12.92	$ 3.36
Expected term	9 years 7 months 6 days		6 years 3 months
Expected forfeiture rate (as a percent)		5.00%	5.00%