Stock-Based Employee Compensation Plans - Vested and unvested options outstanding (Details) - $ / shares	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding, vested (in shares)	358,821		720,402
Options outstanding, unvested (in shares)	233,607
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.01	$ 6.98	$ 6.98	$ 6.86
Options outstanding, weighted average remaining contractual life (years)	6 years 6 months
Options exercisable (in shares)	358,821		720,402
Options exercisable, weighted average exercise price (in dollars per share)	$ 6.74		$ 6.68
Options exercisable, weighted average remaining contractual life	4 years 5 months 12 days
$2.97 – $3.99
Share-based Compensation Arrangement by Share-based Payment Award
Option outstanding, exercise price, lower limit (in dollars per share)	$ 2.97
Option outstanding, exercise price, upper limit (in dollars per share)	$ 3.99
Options outstanding, vested (in shares)	12,000
Options outstanding, unvested (in shares)	0
Options outstanding, weighted average exercise price (in dollars per share)	$ 3.74
Options outstanding, weighted average remaining contractual life (years)	1 year 3 months 25 days
Options exercisable (in shares)	12,000
Options exercisable, weighted average exercise price (in dollars per share)	$ 3.74
$4.00 – $5.99
Share-based Compensation Arrangement by Share-based Payment Award
Option outstanding, exercise price, lower limit (in dollars per share)	4.00
Option outstanding, exercise price, upper limit (in dollars per share)	$ 5.99
Options outstanding, vested (in shares)	16,000
Options outstanding, unvested (in shares)	0
Options outstanding, weighted average exercise price (in dollars per share)	$ 4.34
Options outstanding, weighted average remaining contractual life (years)	6 months 18 days
Options exercisable (in shares)	16,000
Options exercisable, weighted average exercise price (in dollars per share)	$ 4.34
$6.00 – $6.99
Share-based Compensation Arrangement by Share-based Payment Award
Option outstanding, exercise price, lower limit (in dollars per share)	6.00
Option outstanding, exercise price, upper limit (in dollars per share)	$ 6.99
Options outstanding, vested (in shares)	203,489
Options outstanding, unvested (in shares)	5,950
Options outstanding, weighted average exercise price (in dollars per share)	$ 6.61
Options outstanding, weighted average remaining contractual life (years)	4 years 4 months 17 days
Options exercisable (in shares)	203,489
Options exercisable, weighted average exercise price (in dollars per share)	$ 6.60
$7.00 – $7.99
Share-based Compensation Arrangement by Share-based Payment Award
Option outstanding, exercise price, lower limit (in dollars per share)	7.00
Option outstanding, exercise price, upper limit (in dollars per share)	$ 7.99
Options outstanding, vested (in shares)	84,157
Options outstanding, unvested (in shares)	200,000
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.30
Options outstanding, weighted average remaining contractual life (years)	8 years 4 months 17 days
Options exercisable (in shares)	84,157
Options exercisable, weighted average exercise price (in dollars per share)	$ 7.24
$8.00 – $8.40
Share-based Compensation Arrangement by Share-based Payment Award
Option outstanding, exercise price, lower limit (in dollars per share)	8.00
Option outstanding, exercise price, upper limit (in dollars per share)	$ 8.40
Options outstanding, vested (in shares)	43,175
Options outstanding, unvested (in shares)	27,657
Options outstanding, weighted average exercise price (in dollars per share)	$ 8.21
Options outstanding, weighted average remaining contractual life (years)	7 years 4 months 20 days
Options exercisable (in shares)	43,175
Options exercisable, weighted average exercise price (in dollars per share)	$ 8.19