Note 13 - Stock-based Compensation - Stock Option and SARs Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Award Vested and Exercisable [Member]
Options and SARs (in shares)	547	490	475
Exercise price (in dollars per share)	$ 17.43	$ 16.46	$ 15.72
Aggregate intrinsic value	$ 9,710	$ 10,408	$ 14,820
Weighted average fair value (in dollars per share)	$ 3.24	$ 3.16	$ 3.16
Weighted average remaining contractual life (Year)	4 years 109 days	4 years	4 years 109 days
Options and SARs (in shares)	(547)	(490)	(475)
Award Vested and Exercisable [Member] | Minimum [Member]
Exercise price (in dollars per share)	$ 14.02	$ 14.02	$ 14.02
Award Vested and Exercisable [Member] | Maximum [Member]
Exercise price (in dollars per share)	$ 40	$ 33.08	$ 24.56
Award Unvested [Member]
Options and SARs (in shares)	187	214	260
Exercise price (in dollars per share)	$ 30.05	$ 26.46	$ 21.53
Aggregate intrinsic value	$ 1,165	$ 2,515	$ 6,623
Weighted average fair value (in dollars per share)	$ 4.95	$ 4.17	$ 3.43
Weighted average remaining contractual life (Year)	8 years 109 days	7 years 255 days	7 years 292 days
Options and SARs (in shares)	(187)	(214)	(260)
Award Unvested [Member] | Minimum [Member]
Exercise price (in dollars per share)	$ 19.37	$ 15.26	$ 15.24
Award Unvested [Member] | Maximum [Member]
Exercise price (in dollars per share)	$ 40	$ 40	$ 33.08
Award Outstanding [Member]
Options and SARs (in shares)	734	704	735
Exercise price (in dollars per share)	$ 20.64	$ 19.51	$ 17.78
Aggregate intrinsic value	$ 10,875	$ 12,923	$ 21,443
Weighted average fair value (in dollars per share)	$ 3.68	$ 3.47	$ 3.26
Weighted average remaining contractual life (Year)	5 years 109 days	5 years 36 days	5 years 182 days
Options and SARs (in shares)	(734)	(704)	(735)
Award Outstanding [Member] | Minimum [Member]
Exercise price (in dollars per share)	$ 14.02	$ 14.02	$ 14.02
Award Outstanding [Member] | Maximum [Member]
Exercise price (in dollars per share)	$ 40	$ 40	$ 33.08
Award Granted [Member]
Options and SARs (in shares)		46	46
Exercise price (in dollars per share)		$ 35.95	$ 40
Aggregate intrinsic value
Weighted average fair value (in dollars per share)		$ 6.66	$ 6.34
Weighted average remaining contractual life (Year)
Options and SARs (in shares)		(46)	(46)
Award Granted [Member] | Minimum [Member]
Exercise price (in dollars per share)		$ 35.90	$ 40
Award Granted [Member] | Maximum [Member]
Exercise price (in dollars per share)		$ 38.30	$ 40
Award Exercised [Member]
Options and SARs (in shares)		17	77
Exercise price (in dollars per share)		$ 15.57	$ 15.41
Aggregate intrinsic value		$ 362	$ 1,855
Weighted average fair value (in dollars per share)		$ 3.03	$ 3.18
Weighted average remaining contractual life (Year)
Options and SARs (in shares)		(17)	(77)
Award Exercised [Member] | Minimum [Member]
Exercise price (in dollars per share)		$ 15.24	$ 14.02
Award Exercised [Member] | Maximum [Member]
Exercise price (in dollars per share)		$ 15.58	$ 17.89
Award Forfeited [Member]
Options and SARs (in shares)
Exercise price (in dollars per share)
Aggregate intrinsic value
Weighted average fair value (in dollars per share)
Weighted average remaining contractual life (Year)
Options and SARs (in shares)
Award Forfeited [Member] | Minimum [Member]
Exercise price (in dollars per share)
Award Forfeited [Member] | Maximum [Member]
Exercise price (in dollars per share)
Award Vested [Member]
Options and SARs (in shares)	74
Exercise price (in dollars per share)	$ 23.38
Aggregate intrinsic value	$ 914
Weighted average fair value (in dollars per share)	$ 3.77
Weighted average remaining contractual life (Year)
Options and SARs (in shares)	(74)
Award Vested [Member] | Minimum [Member]
Exercise price (in dollars per share)	$ 15.26
Award Vested [Member] | Maximum [Member]
Exercise price (in dollars per share)	$ 40