Note 11 - Share-based Compensation - Stock Option Activity Under Equity Incentive Plans and Director Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common Stock [Member]
Outstanding, number of options (in shares)	1,746,634
Outstanding, weighted average exercise price (in dollars per share)	$ 13.88
Granted, number of options (in shares)	116,276
Granted, weighted average exercise price (in dollars per share)	$ 36.12
Exercised, number of options (in shares)	(468,318)
Exercised, weighted average exercise price (in dollars per share)	$ 12.67
Exercised, aggregate intrinsic value	$ 10,621	$ 2,681	$ 459
Forfeited, number of options (in shares)	(21,383)
Forfeited, weighted average exercise price (in dollars per share)	$ 26.18
Outstanding, number of options (in shares)	1,373,209	1,746,634
Outstanding, weighted average exercise price (in dollars per share)	$ 15.99	$ 13.88
Outstanding, weighted average remaining contractual term (Year)	4 years 332 days
Outstanding, aggregate intrinsic value	$ 30,421
Exercisable, number of options (in shares)	981,069
Weighted average exercise price (in dollars per share)	$ 13.76
Exercisable, weighted average remaining contractual term (Year)	3 years 302 days
Exercisable, aggregate intrinsic value	$ 23,923
Common Class B [Member]
Outstanding, number of options (in shares)	276,716
Outstanding, weighted average exercise price (in dollars per share)	$ 31.78
Exercised, number of options (in shares)	(9,296)	(13,600)	(35,534)
Exercised, weighted average exercise price (in dollars per share)	$ 31.78
Exercised, aggregate intrinsic value	$ 5,937	$ 202	$ 632
Outstanding, number of options (in shares)		276,716
Outstanding, weighted average exercise price (in dollars per share)		$ 31.78
Exercised/Settled in Recapitalization, number of options (in shares)	(276,716)