Note 13 - Stock Based Compensation - Summary of Stock Option Activity (Details) - Employee Stock Option [Member] - $ / shares	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, beginning balance (in shares)	1,158,823	1,106,473	1,051,623	1,051,623
Granted (in shares)		65,663	65,000
Exercised (in shares)	(63,977)	(4,375)	(4,000)
Forfeited or expired (in shares)	(4,815)	(8,938)	(6,150)
Outstanding, ending balance (in shares)	1,090,031	1,158,823	1,106,473	1,090,031
Exercisable (in shares)	378,887			378,887
Outstanding, beginning balance, weighted average exercise price (in dollars per share)	$ 41.40	$ 41.37	$ 41.41	$ 41.41
Granted, weighted average exercise price (in dollars per share)		42.42	39.66
Exercised, weighted average exercise price (in dollars per share)	24.55	25.79	16.25
Forfeited or expired (in dollars per share)	47.84	52.68	46.02
Outstanding, ending balance, weighted average exercise price (in dollars per share)	42.37	$ 41.40	$ 41.37	42.37
Exercisable, weighted average exercise price (in dollars per share)	$ 35.80			$ 35.80