CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Stockholders' equity:
Series C Convertible Preferred Stock, par value (in dollars per share)	$ 0.10	$ 0.10
Series C Convertible Preferred Stock, shares authorized (in shares)	10,000,000	10,000,000
Series C Convertible Preferred Stock, shares issued (in shares)	0	2,103
Series C Convertible Preferred Stock, shares outstanding (in shares)	0	2,103
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common stock shares issued on exercise of options (in shares)	33,801,045	32,932,273
Common stock, shares outstanding (in shares)	33,801,045	32,932,273