Note 5 - Stock-based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Balance, Shares (in shares)	82,670
Balance, Weighted-Average Exercise Price (in dollars per share)	$ 23.37
Balance, Weighted-Average Remaining Contractual Life (Year)	328 days		1 year 36 days
Balance, Aggregate Intrinsic Value	$ 925		$ 1,211
Exercised, Shares (in shares)	(18,040)	(2,110)
Exercised, Weighted-Average Exercise Price (in dollars per share)	$ 23.37
Balance, Shares (in shares)	64,630		82,670
Balance, Weighted-Average Exercise Price (in dollars per share)	$ 23.37		$ 23.37
Exercisable, Shares (in shares)	64,630
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 23.37
Exercisable, Weighted-Average Remaining Contractual Life (Year)	328 days
Exercisable, Aggregate Intrinsic Value	$ 925