Note 13 - Accounting for Stock-based Compensation - Outstanding Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Outstanding, Shares (in shares)	587,407
Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 29.56
Exercisable at December 31, 2016 (in shares)	535,376
Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 28.47
Employee Stock Option [Member]
Outstanding, Shares (in shares)	723,005	766,924	694,552
Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 28.62	$ 28.20	$ 24.34
Exercised, Shares (in shares)	(128,301)	(43,919)	(85,063)
Exercised, Weighted Average Exercise Price (in dollars per share)	$ 23.65	$ 21.23	$ 21.53
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0	0	166,861
Granted, Weighted Average Exercise Price (in dollars per share)			$ 40.68
Forfeited/Expired, Shares (in shares)	(7,297)		(9,426)
Forfeited/Expired, Weighted Average Exercise Price (in dollars per share)	$ 40.68		$ 25.53
Outstanding, Shares (in shares)	587,407	723,005	766,924
Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 29.56	$ 28.62	$ 28.20
Exercised, Shares (in shares)	(128,301)	(43,919)	(85,063)
Outstanding, Intrinsic Value	$ 15,064
Vested plus expected to vest at December 31, 2016 (in shares)	587,204
Vested plus expected to vest, Weighted Average Exercise Price (in dollars per share)	$ 29.55
Vested plus expected to vest, Intrinsic Value	$ 15,061
Exercisable at December 31, 2016 (in shares)	535,376
Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 28.47
Exercisable, Intrinsic Value	$ 14,308