Stock-Based Compensation - Options outstanding and exercisable (Details) - Options	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Exercise Price, $2.89
Options outstanding and exercisable by exercise price
Exercise Price (in dollars per share) | $ / shares	$ 2.89
Number Outstanding (in shares) | shares	183,840
Weighted Average Remaining Contractual Life (in years)	5 years 10 months 24 days
Total Shares Exercisable (in shares) | shares	182,151
Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 2.89
Exercise Price 8.50
Options outstanding and exercisable by exercise price
Exercise Price (in dollars per share) | $ / shares	$ 8.50
Number Outstanding (in shares) | shares	47,883
Weighted Average Remaining Contractual Life (in years)	9 years 10 months 24 days
Total Shares Exercisable (in shares) | shares	125
Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 8.50
Exercise Price, $9.63
Options outstanding and exercisable by exercise price
Exercise Price (in dollars per share) | $ / shares	$ 9.63
Number Outstanding (in shares) | shares	72,340
Weighted Average Remaining Contractual Life (in years)	8 years 6 months
Total Shares Exercisable (in shares) | shares	31,238
Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 9.63
Exercise Price 12.77
Options outstanding and exercisable by exercise price
Exercise Price (in dollars per share) | $ / shares	$ 12.77
Number Outstanding (in shares) | shares	23,175
Weighted Average Remaining Contractual Life (in years)	9 years 8 months 12 days
Total Shares Exercisable (in shares) | shares	2,095
Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 12.77
Exercise Price, $12.96
Options outstanding and exercisable by exercise price
Exercise Price (in dollars per share) | $ / shares	$ 12.96
Number Outstanding (in shares) | shares	58,161
Weighted Average Remaining Contractual Life (in years)	7 years
Total Shares Exercisable (in shares) | shares	54,786
Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 12.93
Exercise Price, $13.16
Options outstanding and exercisable by exercise price
Exercise Price (in dollars per share) | $ / shares	$ 13.16
Number Outstanding (in shares) | shares	181,915
Weighted Average Remaining Contractual Life (in years)	7 years 9 months 18 days
Total Shares Exercisable (in shares) | shares	178,602
Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 13.16
Exercise Price, $17.01
Options outstanding and exercisable by exercise price
Exercise Price (in dollars per share) | $ / shares	$ 17.01
Number Outstanding (in shares) | shares	154,711
Weighted Average Remaining Contractual Life (in years)	9 years
Total Shares Exercisable (in shares) | shares	42,284
Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 17.01
Exercise Price, $17.20
Options outstanding and exercisable by exercise price
Exercise Price (in dollars per share) | $ / shares	$ 17.20
Number Outstanding (in shares) | shares	103,180
Weighted Average Remaining Contractual Life (in years)	9 years 3 months 18 days
Total Shares Exercisable (in shares) | shares	27,927
Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 17.20
Exercise Price 11.24
Options outstanding and exercisable by exercise price
Exercise Price (in dollars per share) | $ / shares	$ 11.24
Number Outstanding (in shares) | shares	825,205
Weighted Average Remaining Contractual Life (in years)	8 years 2 months 12 days
Total Shares Exercisable (in shares) | shares	519,208
Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 9.85