Stock Option and Incentive Plans (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Stock option
2005 Stock option and incentive plans
Contractual life	7 years 4 months 24 days
Shares
Outstanding at the beginning of the period (in shares)	1,093,208	689,663
Granted (in shares)	700,000	589,719
Exercised (in shares)	(122,634)	(15,515)
Forfeited (in shares)		(170,659)
Outstanding at the end of the period (in shares)	1,670,574	1,093,208
Exercisable at the end of the period (in shares)	764,338
Exercisable and expected to vest at the end of the year (in shares)	1,670,574
Weighted-Average Exercise Price Per Share
Outstanding at the beginning of the period (in dollars per share)	$ 1.04
Granted (in dollars per share)	$ 8.99
Exercised (in dollars per share)	$ 1.04	$ 1.04
Outstanding at the end of the period (in dollars per share)	$ 4.37	$ 1.04
Exercisable at the end of the period (in dollars per share)	$ 1.75
Exercisable and expected to vest at the end of the year (in dollars per share)	$ 4.37
Aggregate Intrinsic Value
Outstanding at the end of the period	$ 10,357
Exercisable at the end of the period	6,740
Exercisable and expected to vest at the end of the year	10,357
Additional Disclosures
Weighted average remaining contractual term	8 years 7 months 6 days
Weighted average remaining contractual term exercisable	7 years 4 months 24 days
Weighted average grant date fair value (in dollars per share)	$ 6.09	$ 0.85
Weighted-average assumptions
Expected annual dividend yield (as a percent)	0.00%	0.00%
Unrecognized compensation expense
Unrecognized compensation expense	4,082
Stock option | Recognition Period One
Unrecognized compensation expense
Unrecognized compensation expense	1,448
Stock option | Recognition Period Two
Unrecognized compensation expense
Unrecognized compensation expense	1,302
Stock option | Recognition Period Three
Unrecognized compensation expense
Unrecognized compensation expense	929
Stock option | Recognition Period Four
Unrecognized compensation expense
Unrecognized compensation expense	$ 403
Stock option | Maximum
Weighted-average assumptions
Expected stock price volatility (as a percent)	86.08%	118.00%
Expected term of options	6 years 22 days	6 years 3 months
Risk-free interest rate (as a percent)	1.98%	1.75%
Stock option | Minimum
Weighted-average assumptions
Expected stock price volatility (as a percent)	77.66%	103.90%
Expected term of options	5 years 6 months	5 years
Risk-free interest rate (as a percent)	1.75%	0.84%
2005 Plan
Shares
Outstanding at the end of the period (in shares)	970,574
2005 Plan | Stock option | Maximum
2005 Stock option and incentive plans
Contractual life	10 years
Vesting period	4 years
Additional Disclosures
Weighted average remaining contractual term exercisable	10 years
2014 Plan
Shares
Outstanding at the end of the period (in shares)	700,000
2014 Plan | Stock option | Maximum
2005 Stock option and incentive plans
Contractual life	10 years
Vesting period	4 years
Additional Disclosures
Weighted average remaining contractual term exercisable	10 years