CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Preferred Stock Series A Convertible Preferred Stock	Preferred Stock Series B Redeemable Convertible Preferred Stock	Preferred Stock Series C Redeemable Convertible Preferred Stock	Preferred Stock Series D Redeemable Convertible Preferred Stock	Common Stock Class B Common Stock	Additional Paid-in Capital	Accumulated Deficit	Total
Balance, beginning of period at Dec. 31, 2019	$ 1,253	$ 10,780	$ 28,067	$ 25,500	$ 1		$ (31,413)	$ (30,159)
Balance, beginning of period (in shares) at Dec. 31, 2019	5,013,333	13,715,330	26,732,361	16,390,217	2,286,872
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options						$ 2		2
Exercise of stock options (in shares)					5,495
Accrued dividends		$ 180	$ 510	$ 500		(314)	(876)	(1,190)
Net loss							(2,143)	(2,143)
Stock-based compensation						312		312
Balance, end of period at Mar. 31, 2020	$ 1,253	$ 10,960	$ 28,577	$ 26,000	$ 1		(34,432)	(33,178)
Balance, end of period (in shares) at Mar. 31, 2020	5,013,333	13,715,330	26,732,361	16,390,217	2,292,367
Balance, beginning of period at Dec. 31, 2020	$ 1,253	$ 11,500	$ 30,107	$ 27,500	$ 1		(52,280)	(51,026)
Balance, beginning of period (in shares) at Dec. 31, 2020	5,013,333	13,715,330	26,732,361	16,390,217	2,563,765
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options						44		44
Exercise of stock options (in shares)					271,334
Accrued dividends		$ 180	$ 510	$ 500		(298)	(892)	(1,190)
Net loss							(8,082)	(8,082)
Stock-based compensation						$ 254		254
Balance, end of period at Mar. 31, 2021	$ 1,253	$ 11,680	$ 30,617	$ 28,000	$ 1		$ (61,254)	$ (60,000)
Balance, end of period (in shares) at Mar. 31, 2021	5,013,333	13,715,330	26,732,361	16,390,217	2,835,099