Note 7 - Share-based Compensation - Stock Option Activity (Details) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Share-based Payment Arrangement, Option [Member]
Outstanding at beginning of period (in shares)	1,570,455
Outstanding at beginning of period (in dollars per share)	$ 1.96
Granted (in shares)	0	0
Granted, weighted average exercise price (in dollars per share)
Exercised (in shares)	(251,180)
Exercised, weighted average exercise price (in dollars per share)	$ 1.84
Forfeited (in shares)
Forfeited, weighted average exercise price (in dollars per share)
Expired (in shares)
Expired, weighted average exercise price (in dollars per share)
Outstanding (in shares)	1,319,275	1,570,455
Outstanding at beginning of year, weighted average exercise price (in dollars per share)	$ 1.98	$ 1.96
Service vesting-based stock options exercisable at March 31, 2020 (in shares)	1,263,377
Service vesting-based stock options exercisable at March 31, 2020 (in dollars per share)	$ 1.96
Performance Shares [Member]
Outstanding at beginning of period (in shares)	737,497
Outstanding at beginning of period (in dollars per share)	$ 1.64
Granted (in shares)
Granted, weighted average exercise price (in dollars per share)
Exercised (in shares)	(17,113)
Exercised, weighted average exercise price (in dollars per share)	$ 1.64
Outstanding (in shares)	720,384	737,497
Outstanding at beginning of year, weighted average exercise price (in dollars per share)	$ 1.64	$ 1.64
Service vesting-based stock options exercisable at March 31, 2020 (in shares)	720,384
Service vesting-based stock options exercisable at March 31, 2020 (in dollars per share)	$ 1.64