Stock-Based Employee Compensation Plans - Vested and unvested options outstanding (Details) - $ / shares	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding, vested (in shares)	314,112		721,420
Options outstanding, unvested (in shares)	285,618
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.02	$ 6.98	$ 6.88	$ 6.86
Options outstanding, weighted average remaining contractual life (years)	6 years 8 months 23 days
Options exercisable (in shares)	314,112		721,420
Options exercisable, weighted average exercise price (in dollars per share)	$ 6.66		$ 6.68
Options exercisable, weighted average remaining contractual life	4 years 8 months 19 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 6 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)	9 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)	207,739
Options outstanding, unvested (in shares)	6,400
Options outstanding, weighted average exercise price (in dollars per share)	$ 6.61
Options outstanding, weighted average remaining contractual life (years)	4 years 7 months 17 days
Options exercisable (in shares)	207,739
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)	34,157
Options outstanding, unvested (in shares)	250,000
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.30
Options outstanding, weighted average remaining contractual life (years)	8 years 7 months 17 days
Options exercisable (in shares)	34,157
Options exercisable, weighted average exercise price (in dollars per share)	$ 7.10
$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)	44,216
Options outstanding, unvested (in shares)	29,218
Options outstanding, weighted average exercise price (in dollars per share)	$ 8.22
Options outstanding, weighted average remaining contractual life (years)	7 years 7 months 24 days
Options exercisable (in shares)	44,216
Options exercisable, weighted average exercise price (in dollars per share)	$ 8.20