Note 7 - Stock-based Compensation - Summary of Restricted Common Stock Activity (Details) - $ / shares	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Restricted Stock [Member]
Outstanding, Shares (in shares)	1,035,728	917,533
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 19.69	$ 16.84
Granted, Shares (in shares)	333,382	296,042
Granted, Weighted average grant date fair value (in dollars per share)	$ 22.16	$ 18.21
Vested, Shares (in shares)	(294,558)	(502,241)
Vested, Weighted average grant date fair value (in dollars per share)	$ 18.56	$ 16.10
Outstanding, Shares (in shares)	1,074,552	711,334
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 20.76	$ 17.94
Restricted Stock [Member] | Common Class A [Member]
Outstanding, Shares (in shares)	720,421	480,042
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 18.22	$ 16.10
Granted, Shares (in shares)	250,448	233,425
Granted, Weighted average grant date fair value (in dollars per share)	$ 20.52	$ 17.67
Vested, Shares (in shares)	(229,758)	(248,539)
Vested, Weighted average grant date fair value (in dollars per share)	$ 16.99	$ 15.00
Outstanding, Shares (in shares)	741,111	464,928
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 19.38	$ 17.47
Restricted Stock Units (RSUs) [Member]
Outstanding, Shares (in shares)	125,247	90,184
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 19.02	$ 18.92
Granted, Shares (in shares)	259,079	95,115
Granted, Weighted average grant date fair value (in dollars per share)	$ 23.87	$ 19.05
Vested, Shares (in shares)	(108,921)	(60,052)
Vested, Weighted average grant date fair value (in dollars per share)	$ 19.03	$ 18.92
Forfeited, Shares (in shares)	(1,260)	0
Forfeited, Weighted average grant date fair value (in dollars per share)	$ 19.05	$ 0
Outstanding, Shares (in shares)	274,145	125,247
Outstanding, Weighted average grant date fair value (in dollars per share)	$ 23.60	$ 19.02