Note 8 - Shareholders' Equity - Summary of Nonvested Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Nonvested at January 1, 2017 (in shares)	553,000
Nonvested at January 1, 2017 (in dollars per share)	$ 5.80
Granted (in shares)	266,000	325,000	343,000
Granted (in dollars per share)	$ 8.27
Vested (in shares)	(258,000)
Vested (in dollars per share)	$ 5.78
Forfeited (in shares)
Nonvested at December 31, 2017 (in shares)	561,000	553,000
Nonvested at December 31, 2017 (in dollars per share)	$ 6.98