Note 7 - Stock-based Compensation - Restricted Stock Units (Details)	9 Months Ended
	Sep. 30, 2022 $ / shares shares
Time-based Restricted Stock Units [Member]
Balance (in shares) | shares	235,944
Balance, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 32.38
Granted (in shares) | shares	65,389
Granted, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 46.85
Vested (in shares) | shares	(87,554)
Vested, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 40.89
Forfeited (in shares) | shares	(11,182)
Forfeited, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 33.31
Balance (in shares) | shares	202,597
Balance, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 33.32
Performance-based Restricted Stock Units [Member]
Balance (in shares) | shares	332,506
Balance, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 31.82
Granted (in shares) | shares	112,393
Granted, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 40.24
Vested (in shares) | shares	(81,934)
Vested, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 44.52
Forfeited (in shares) | shares	0
Forfeited, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 0
Balance (in shares) | shares	362,965
Balance, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 31.56