Note 13 - Stock-based Compensation - Information about Stock Options Outstanding (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Options outstanding, vested and expected to vest, number outstanding (in shares)	233,384	229,531	276,266	252,616
Options outstanding, vested and expected to vest, weighted average exercise price (in dollars per share)	$ 97.78	$ 86.46	$ 72.38	$ 64.71
Exercise Price Range One [Member]
Range of exercise prices, lower limit (in dollars per share)	$ 7.76
Options outstanding, vested and expected to vest, number outstanding (in shares)	4,624
Range of exercise prices, upper limit (in dollars per share)	$ 31.43
Options outstanding, vested and expected to vest, weighted average remaining contractual life (Year)	4 months 6 days
Options outstanding, vested and expected to vest, weighted average exercise price (in dollars per share)	$ 30.58
Options exercisable, number exercisable (in shares)	4,624
Options exercisable, weighted average exercise price (in dollars per share)	$ 30.58
Exercise Price Range Two [Member]
Range of exercise prices, lower limit (in dollars per share)	$ 31.44
Options outstanding, vested and expected to vest, number outstanding (in shares)	50,159
Range of exercise prices, upper limit (in dollars per share)	$ 66.87
Options outstanding, vested and expected to vest, weighted average remaining contractual life (Year)	3 years 6 months 29 days
Options outstanding, vested and expected to vest, weighted average exercise price (in dollars per share)	$ 57.13
Options exercisable, number exercisable (in shares)	45,986
Options exercisable, weighted average exercise price (in dollars per share)	$ 57.02
Exercise Price Range Three [Member]
Range of exercise prices, lower limit (in dollars per share)	$ 66.88
Options outstanding, vested and expected to vest, number outstanding (in shares)	41,586
Range of exercise prices, upper limit (in dollars per share)	$ 96.20
Options outstanding, vested and expected to vest, weighted average remaining contractual life (Year)	7 years 9 months 25 days
Options outstanding, vested and expected to vest, weighted average exercise price (in dollars per share)	$ 89.95
Options exercisable, number exercisable (in shares)	9,570
Options exercisable, weighted average exercise price (in dollars per share)	$ 71.68
Exercise Price Range Four [Member]
Range of exercise prices, lower limit (in dollars per share)	$ 96.21
Options outstanding, vested and expected to vest, number outstanding (in shares)	137,015
Range of exercise prices, upper limit (in dollars per share)	$ 123.10
Options outstanding, vested and expected to vest, weighted average remaining contractual life (Year)	7 years 8 months 1 day
Options outstanding, vested and expected to vest, weighted average exercise price (in dollars per share)	$ 117.31
Options exercisable, number exercisable (in shares)	55,520
Options exercisable, weighted average exercise price (in dollars per share)	$ 107.28