Note 10 - Stockholders' Equity and Stock-based Compensation - Stock Option Plan Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Balance (in shares) | shares	2,866,675
Balance, weighted average exercise price (in dollars per share) | $ / shares	$ 40.54
Weighted average remaining contractual life (Year)	6 years	6 years
Balance, aggregate intrinsic value | $	$ 120,055	$ 125,647
Granted (in shares) | shares	269,950
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 107.01
Exercised (in shares) | shares	(695,468)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 34.46
Canceled (in shares) | shares	(84,486)
Canceled, weighted average exercise price (in dollars per share) | $ / shares	$ 86.08
Balance (in shares) | shares	2,356,671	2,866,675
Balance, weighted average exercise price (in dollars per share) | $ / shares	$ 48.32	$ 40.54
Vested and expected to vest (in shares) | shares	2,208,860
Vested and expected to vest, weighted average exercise price (in dollars per share) | $ / shares	$ 45.07
Weighted Average Remaining Contractual Life (Years), Vested and Expected to Vest (Year)	5 years 9 months 18 days
Vested and expected to vest Aggregate intrinsic value, Vested and expected to vest | $	$ 118,883
Exercisable (in shares) | shares	1,666,292
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 30.49
Weighted Average Remaining Contractual Life (Years), Exercisable (Year)	4 years 9 months 18 days
Aggregate intrinsic value, Exercisable | $	$ 112,502