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	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Number of Shares Subject to Options
Unvested, end of period (in shares)	285,618
Stock options
Number of Shares Subject to Options
Unvested, beginning of period (in shares)	334,322	275,457
Granted (in shares)	0	0
Vested (in shares)	(34,809)	(147,687)
Forfeited/canceled (in shares)	(13,895)	(6,744)
Unvested, end of period (in shares)	285,618	121,026
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	0
Vested (in dollars per share)	2.78	2.79
Forfeited/canceled (in dollars per share)	2.81	2.83
Unvested, end of period (in dollars per share)	$ 2.09	$ 2.79