Note 7 - Stock-based Compensation - Restricted Stock Units (Details)	3 Months Ended
	Mar. 31, 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	(17,063)
Vested, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 46.29
Forfeited (in shares) | shares	(1,677)
Forfeited, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 30.09
Balance (in shares) | shares	282,593
Balance, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 34.90
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	0
Granted, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 0
Vested (in shares) | shares	0
Vested, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 0
Forfeited (in shares) | shares	0
Forfeited, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 0
Balance (in shares) | shares	332,506
Balance, weighted-average grant date fair value (in dollars per share) | $ / shares	$ 31.82