Note 13 - Stock-based Compensation - Performance Stock (Details) - Performance Shares [Member] - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Performance stock (in shares)	16,839	19,956	9,383
Restricted stock, weighted-average grant date fair value (in dollars per share)	$ 115.56	$ 118.66	$ 58.35
Granted (in shares)	35,697	15,078	19,956
Granted, weighted-average grant date fair value (in dollars per share)	$ 96.71	$ 203.64	$ 118.66
Restrictions lapsed (in shares)	0	0	(7,113)
Restrictions lapsed, weighted-average grant date fair value (in dollars per share)	$ 0	$ 0	$ 58.35
Performance change (in shares)	(13,156)	(10,366)	0
Performance change, weighted-average grant date fair value (in dollars per share)	$ 99.59	$ 192.95	$ 0
Forfeited (in shares)	(3,578)	(7,829)	(2,270)
Forfeited, weighted-average grant date fair value (in dollars per share)	$ 121.79	$ 113.91	$ 58.35
Granted (in shares)	35,697	15,078	19,956
Restrictions lapsed (in shares)	0	0	(7,113)
Performance change, weighted-average grant date fair value (in dollars per share)	$ 99.59	$ 192.95	$ 0
Forfeited (in shares)	(3,578)	(7,829)	(2,270)
Performance stock (in shares)	35,802	16,839	19,956
Restricted stock, weighted-average grant date fair value (in dollars per share)	$ 77.91	$ 115.56	$ 118.66