Note 14 - Stock Option Plans - Stock Option Transactions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Outstanding, Number of shares (in shares)	702,337	653,571	474,501
Outstanding, Weighted average exercise price per share (in dollars per share)	$ 43.80	$ 36.69	$ 12.67
Granted, Number of shares (in shares)	180,800	163,366	370,025
Granted, Weighted average exercise price per share (in dollars per share)	$ 60.56	$ 62.80	$ 54.10
Exercised, Number of shares (in shares)	(80,319)	(63,886)	(172,759)
Exercised, Weighted average exercise price per share (in dollars per share)	$ 16.90	$ 12.86	$ 7.88
Forfeited, Number of shares (in shares)	(31,986)	(50,714)	(18,196)
Forfeited, Weighted average exercise price per share (in dollars per share)	$ 59.35	$ 52.33	$ 37.70
Expired, Number of shares (in shares)	(16,335)
Expired, Weighted average exercise price per share (in dollars per share)	$ 47.51
Outstanding, Number of shares (in shares)	754,497	702,337	653,571
Outstanding, Weighted average exercise price per share (in dollars per share)	$ 49.94	$ 43.80	$ 36.69
Options exercisable, Number of shares (in shares)	356,066	326,937	243,771
Options exercisable, Weighted average exercise price per share (in dollars per share)	$ 40.64	$ 28.91	$ 14.79