Note 12 - Share-based Compensation - Stock Options Outstanding (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Lower range of exercise prices on options (in dollars per share)	$ 3.82
Upper range of exercise prices on options (in dollars per share)	$ 21.63
Options outstanding (in shares) | shares	633,877
Weighted average remaining contractual life on options (Year)	3 years 306 days
Weighted average exercise price on options (in dollars per share)	$ 13.33
Exercise Price Range 1 [Member]
Lower range of exercise prices on options (in dollars per share)	3.82
Upper range of exercise prices on options (in dollars per share)	$ 5.55
Options outstanding (in shares) | shares	59,000
Weighted average remaining contractual life on options (Year)	2 years 29 days
Weighted average exercise price on options (in dollars per share)	$ 4.81
Exercise Price Range 2 [Member]
Lower range of exercise prices on options (in dollars per share)	5.65
Upper range of exercise prices on options (in dollars per share)	$ 7.36
Options outstanding (in shares) | shares	151,995
Weighted average remaining contractual life on options (Year)	1 year 350 days
Weighted average exercise price on options (in dollars per share)	$ 6.65
Exercise Price Range 3 [Member]
Lower range of exercise prices on options (in dollars per share)	7.96
Upper range of exercise prices on options (in dollars per share)	$ 10.38
Options outstanding (in shares) | shares	45,100
Weighted average remaining contractual life on options (Year)	4 years 193 days
Weighted average exercise price on options (in dollars per share)	$ 8.87
Exercise Price Range 4 [Member]
Lower range of exercise prices on options (in dollars per share)	16.35
Upper range of exercise prices on options (in dollars per share)	$ 21.63
Options outstanding (in shares) | shares	377,782
Weighted average remaining contractual life on options (Year)	4 years 288 days
Weighted average exercise price on options (in dollars per share)	$ 17.88