Stock Option and Incentive Plans - Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Stock option
Stock option and incentive plans
Contractual life	7 years 8 months 12 days
Shares
Outstanding at the beginning of the period (in shares)	1,670,574	1,093,208
Granted (in shares)	585,800	700,000
Exercised (in shares)	(327,098)	(122,634)
Forfeited (in shares)	(44,950)
Expired (in shares)	(85,100)
Outstanding at the end of the period (in shares)	1,799,226	1,670,574
Exercisable at the end of the period (in shares)	785,174
Exercisable and expected to vest at the end of the year (in shares)	1,799,226
Weighted-Average Exercise Price Per Share
Outstanding at the beginning of the period (in dollars per share)	$ 4.37	$ 1.04
Granted (in dollars per share)	12.56	8.99
Exercised (in dollars per share)	1.14	1.04
Forfeited (in dollars per share)	6.13
Expired (in dollars per share)	1.04
Outstanding at the end of the period (in dollars per share)	7.74	4.37
Exercisable at the end of the period (in dollars per share)	5.05
Exercisable and expected to vest at the end of the year (in dollars per share)	$ 7.74
Aggregate Intrinsic Value
Outstanding at the end of the period	$ 3,786
Exercisable at the end of the period	2,834
Exercisable and expected to vest at the end of the year	$ 3,786
Additional Disclosures
Weighted average remaining contractual term	8 years 6 months
Weighted average remaining contractual term exercisable	7 years 8 months 12 days
Weighted average grant date fair value (in dollars per share)	$ 8.15	$ 6.09
Weighted-average assumptions
Expected annual dividend yield (as a percent)	0.00%	0.00%
Unrecognized compensation expense
Unrecognized compensation expense	$ 6,558
Stock option | Recognition Period One
Unrecognized compensation expense
Unrecognized compensation expense	2,863
Stock option | Recognition Period Two
Unrecognized compensation expense
Unrecognized compensation expense	2,256
Stock option | Recognition Period Three
Unrecognized compensation expense
Unrecognized compensation expense	1,293
Stock option | Recognition Period Four
Unrecognized compensation expense
Unrecognized compensation expense	$ 146
Stock option | Minimum
Weighted-average assumptions
Expected stock price volatility (as a percent)	73.64%	77.66%
Expected term of options	5 years 2 months 12 days	5 years 6 months
Risk-free interest rate (as a percent)	1.44%	1.75%
Stock option | Maximum
Weighted-average assumptions
Expected stock price volatility (as a percent)	81.21%	86.08%
Expected term of options	6 years 1 month 6 days	6 years 22 days
Risk-free interest rate (as a percent)	1.92%	1.98%
2005 Plan
Shares
Outstanding at the end of the period (in shares)	549,287
2005 Plan | Stock option | Maximum
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)	1,249,939
2014 Plan | Stock option | Maximum
Stock option and incentive plans
Contractual life	10 years
Vesting period	4 years
Additional Disclosures
Weighted average remaining contractual term exercisable	10 years