Stock-Based Employee Compensation Plans - Summary of status of unvested options and changes in number of shares subject to and in weighted average grant date fair values of unvested options (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Number of Shares Subject to Options
Unvested, end of period (in shares)	233,607		233,607
Stock options
Number of Shares Subject to Options
Unvested, beginning of period (in shares)			334,322	275,457
Granted (in shares)			0	250,000
Vested (in shares)			(84,809)	(150,439)
Forfeited/canceled (in shares)			(15,906)	(6,744)
Unvested, end of period (in shares)	233,607	368,274	233,607	368,274
Weighted Average Grant Date Fair Value Per Share
Unvested, beginning of period (in dollars per share)			$ 2.19	$ 2.79
Granted (in dollars per share)	$ 0	$ 1.97	0	1.97
Vested (in dollars per share)			2.32	2.79
Forfeited/canceled (in dollars per share)			2.81	2.83
Unvested, end of period (in dollars per share)	$ 2.10	$ 2.23	$ 2.10	$ 2.23