Note 8 - Stockholders' Equity - Option Activity for Stock Option Plans (Details)	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares
Outstanding, options (in shares) | shares	302,368
Outstanding, weighted average exercise price, options (in dollars per share) | $ / shares	$ 13.99
Granted, options (in shares) | shares	10,200
Granted, weighted average exercise price, options (in dollars per share) | $ / shares	$ 4.38
Forfeited, options (in shares) | shares	(16,539)
Forfeited, weighted average exercise price, options (in dollars per share) | $ / shares	$ 11.50
Outstanding, options (in shares) | shares	296,029
Outstanding, weighted average exercise price, options (in dollars per share) | $ / shares	$ 13.80
Outstanding, weighted average remaining contractual life, options (Year)	8 years 219 days
Outstanding, aggregate intrinsic value, options | $	$ 763,499
Vested and Expected to Vest, options (in shares) | shares	215,932
Vested and Expected to Vest, weighted average exercise price, options (in dollars per share) | $ / shares	$ 15.95
Vested and Expected to Vest, weighted average remaining contractual life, options (Year)	8 years 146 days
Vested and Expected to Vest, aggregate intrinsic value, options | $	$ 525,700
Exercisable, options (in shares) | shares	94,978
Exercisable, weighted average exercise price, options (in dollars per share) | $ / shares	$ 25.70
Exercisable, weighted average remaining contractual life, options (Year)	7 years 219 days
Exercisable, aggregate intrinsic value, options | $	$ 171,726