Note 15 - Stock-based Compensation - Summary of Information About Stock-based Awards Outstanding (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Number of shares outstanding (in shares)	2,527	1,548
Weighted average remaining contractual life in years, options outstanding (Year)	4 years 109 days	4 years 73 days
Aggregate intrinsic value, options outstanding	$ 17,283	$ 34,990
Number of shares exercisable (in shares)	846	432
Weighted average remaining contractual life in years, options exercisable (Year)	3 years 109 days	3 years
Aggregate intrinsic value, options exercisable	$ 9,389	$ 13,523
Exercise Price 1 [Member]
Exercise price (in dollars per share)
Number of shares outstanding (in shares)	75	23
Weighted average remaining contractual life in years, options outstanding (Year)	1 year 292 days	3 years 328 days
Aggregate intrinsic value, options outstanding	$ 3,933	$ 1,455
Number of shares exercisable (in shares)
Weighted average remaining contractual life in years, options exercisable (Year)
Aggregate intrinsic value, options exercisable
Exercise Price 2 [Member]
Exercise price (in dollars per share)	$ 20.13	$ 20.13
Number of shares outstanding (in shares)	29	35
Weighted average remaining contractual life in years, options outstanding (Year)	109 days	1 year 109 days
Aggregate intrinsic value, options outstanding	$ 924	$ 1,533
Number of shares exercisable (in shares)	29	35
Weighted average remaining contractual life in years, options exercisable (Year)	109 days	1 year 109 days
Aggregate intrinsic value, options exercisable	$ 924	$ 1,533
Exercise Price 3 [Member]
Exercise price (in dollars per share)	$ 23.34	$ 23.34
Number of shares outstanding (in shares)	99	176
Weighted average remaining contractual life in years, options outstanding (Year)	146 days	1 year 146 days
Aggregate intrinsic value, options outstanding	$ 2,897	$ 7,150
Number of shares exercisable (in shares)	99	176
Weighted average remaining contractual life in years, options exercisable (Year)	146 days	1 year 146 days
Aggregate intrinsic value, options exercisable	$ 2,897	$ 7,150
Exercise Price 5 [Member]
Exercise price (in dollars per share)	$ 35.15	$ 35.15
Number of shares outstanding (in shares)	15	15
Weighted average remaining contractual life in years, options outstanding (Year)	4 years 36 days	5 years 36 days
Aggregate intrinsic value, options outstanding	$ 257	$ 432
Number of shares exercisable (in shares)	15	15
Weighted average remaining contractual life in years, options exercisable (Year)	4 years 36 days	5 years 36 days
Aggregate intrinsic value, options exercisable	$ 257	$ 432
Exercise Price 4 [Member]
Exercise price (in dollars per share)		$ 25.65
Number of shares outstanding (in shares)		10
Weighted average remaining contractual life in years, options outstanding (Year)		109 days
Aggregate intrinsic value, options outstanding		$ 398
Number of shares exercisable (in shares)		10
Weighted average remaining contractual life in years, options exercisable (Year)		109 days
Aggregate intrinsic value, options exercisable		$ 398
Exercise Price 6 [Member]
Exercise price (in dollars per share)	$ 38.24	$ 38.24
Number of shares outstanding (in shares)	15	15
Weighted average remaining contractual life in years, options outstanding (Year)	3 years 292 days	4 years 292 days
Aggregate intrinsic value, options outstanding	$ 211	$ 386
Number of shares exercisable (in shares)	15	15
Weighted average remaining contractual life in years, options exercisable (Year)	3 years 292 days	4 years 292 days
Aggregate intrinsic value, options exercisable	$ 211	$ 386
Exercise Price 7 [Member]
Exercise price (in dollars per share)	$ 42.87	$ 42.87
Number of shares outstanding (in shares)	942	1,074
Weighted average remaining contractual life in years, options outstanding (Year)	3 years 182 days	4 years 182 days
Aggregate intrinsic value, options outstanding	$ 8,879	$ 22,651
Number of shares exercisable (in shares)	521	143
Weighted average remaining contractual life in years, options exercisable (Year)	3 years 182 days	4 years 182 days
Aggregate intrinsic value, options exercisable	$ 4,918	$ 3,005
Exercise Price 8 [Member]
Exercise price (in dollars per share)	$ 47.46	$ 47.46
Number of shares outstanding (in shares)	38	38
Weighted average remaining contractual life in years, options outstanding (Year)	4 years 328 days	5 years 328 days
Aggregate intrinsic value, options outstanding	$ 182	$ 619
Number of shares exercisable (in shares)	38	38
Weighted average remaining contractual life in years, options exercisable (Year)	4 years 328 days	5 years 328 days
Aggregate intrinsic value, options exercisable	$ 182	$ 619
Exercise Price 9 [Member]
Exercise price (in dollars per share)	$ 53.16	$ 57.97
Number of shares outstanding (in shares)	35	30
Weighted average remaining contractual life in years, options outstanding (Year)	5 years 328 days	6 years 219 days
Aggregate intrinsic value, options outstanding		$ 180
Number of shares exercisable (in shares)
Weighted average remaining contractual life in years, options exercisable (Year)
Aggregate intrinsic value, options exercisable
Exercise Price 10 [Member]
Exercise price (in dollars per share)	$ 53.44	$ 58.79
Number of shares outstanding (in shares)	828	23
Weighted average remaining contractual life in years, options outstanding (Year)	5 years 182 days	4 years 182 days
Aggregate intrinsic value, options outstanding		$ 120
Number of shares exercisable (in shares)
Weighted average remaining contractual life in years, options exercisable (Year)
Aggregate intrinsic value, options exercisable
Exercise Price 11 [Member]
Exercise price (in dollars per share)	$ 55.16	$ 63.35
Number of shares outstanding (in shares)	296	109
Weighted average remaining contractual life in years, options outstanding (Year)	4 years 328 days	5 years 328 days
Aggregate intrinsic value, options outstanding		$ 66
Number of shares exercisable (in shares)	66
Weighted average remaining contractual life in years, options exercisable (Year)	4 years 328 days
Aggregate intrinsic value, options exercisable
Exercise Price 12 [Member]
Exercise price (in dollars per share)	$ 57.97
Number of shares outstanding (in shares)	30
Weighted average remaining contractual life in years, options outstanding (Year)	5 years 219 days
Aggregate intrinsic value, options outstanding
Number of shares exercisable (in shares)	30
Weighted average remaining contractual life in years, options exercisable (Year)	5 years 219 days
Aggregate intrinsic value, options exercisable
Exercise Price 13 [Member]
Exercise price (in dollars per share)	$ 58.79
Number of shares outstanding (in shares)	16
Weighted average remaining contractual life in years, options outstanding (Year)	3 years 182 days
Aggregate intrinsic value, options outstanding
Number of shares exercisable (in shares)
Weighted average remaining contractual life in years, options exercisable (Year)
Aggregate intrinsic value, options exercisable
Exercise Price 14 [Member]
Exercise price (in dollars per share)	$ 63.35
Number of shares outstanding (in shares)	109
Weighted average remaining contractual life in years, options outstanding (Year)	4 years 328 days
Aggregate intrinsic value, options outstanding
Number of shares exercisable (in shares)	33
Weighted average remaining contractual life in years, options exercisable (Year)	4 years 328 days
Aggregate intrinsic value, options exercisable