Note 13 - Stock-based Compensation - Summary of Option Activity (Details) - Lindblad Plan and 2015 Plan [Member] - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options outstanding, shares (in shares)	1,175,424	2,130,848	2,849,071
Options outstanding, weighted average exercise price (in dollars per share)	$ 3.23	$ 2.57	$ 2.69
Options outstanding, weighted average contractual ife (Year)	7 years 219 days	2 years 146 days	2 years 292 days	3 years 255 days
Options outstanding, aggregate intrinsic value	$ 842,000	$ 7,707,255	$ 146,542,221	$ 23,992,814
Granted, shares (in shares)			220,000
Granted, weighted average exercise price (in dollars per share)			$ 9.63
Exercised, shares (in shares)	(955,424)	(955,424)	(638,223)
Exercised, weighted average exercise price (in dollars per share)	$ 1.76	$ 1.76	$ 1.76
Forfeited, shares (in shares)			(300,000)
Forfeited, weighted average exercise price (in dollars per share)			$ 10.58
Options outstanding, shares (in shares)	220,000	1,175,424	2,130,848	2,849,071
Options outstanding, weighted average exercise price (in dollars per share)	$ 9.63	$ 3.23	$ 2.57	$ 2.69
Options vested and/or expected to vest, number of options (in shares)	220,000
Options vested and/or expected to vest, weighted average exercise price (in dollars per share)	$ 9.63
Options vested and/or expected to vest, weighted average contractual life (Year)	7 years 219 days
Options vested and/or expected to vest, aggregate intrinsic value	$ 842,000
Options exercisable, number of options (in shares)	113,333
Options exercisable, weighted average exercise price (in dollars per share)	$ 9.68
Options exercisable, weighted average contractual life (Year)	7 years 219 days
Options exercisable, aggregate intrinsic value	$ 428,333