Note 10 - Net Income Per Share - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Net income	$ 27,660	$ 26,596	$ 25,410	$ 27,769	$ 21,142	$ 228	$ 79,666	$ 49,139
Basic weighted average shares (in shares)	38,317			38,925			38,680	39,077
Stock options (in shares)	658			852			715	851
Restricted stock units (in shares)	242			161			236	219
Employee stock purchase plan (in shares)	3			0			3	0
Diluted weighted average shares (in shares)	39,220			39,938			39,634	40,147
Basic (in dollars per share)	$ 0.72			$ 0.71			$ 2.06	$ 1.26
Diluted (in dollars per share)	$ 0.71			$ 0.70			$ 2.01	$ 1.22