Note 6 - Share-based Compensation - Summary of Information About Stock Options Outstanding (Details)	3 Months Ended
	Mar. 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)	$ 18.66
Options outstanding (in shares) | shares	859,139
Weighted Average Remaining Contractual Life on options (Year)	3 years 156 days
Weighted Average Exercise Price on options (in dollars per share)	$ 11.35
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	74,166
Weighted Average Remaining Contractual Life on options (Year)	2 years 251 days
Weighted Average Exercise Price on options (in dollars per share)	$ 4.75
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	341,057
Weighted Average Remaining Contractual Life on options (Year)	1 year 335 days
Weighted Average Exercise Price on options (in dollars per share)	$ 6.58
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	61,700
Weighted Average Remaining Contractual Life on options (Year)	4 years 178 days
Weighted Average Exercise Price on options (in dollars per share)	$ 9.28
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)	$ 18.66
Options outstanding (in shares) | shares	382,216
Weighted Average Remaining Contractual Life on options (Year)	4 years 273 days
Weighted Average Exercise Price on options (in dollars per share)	$ 17.22