Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - $ / shares	Jun. 30, 2021	Dec. 31, 2020
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, authorized (in shares)	1,000,000	1,000,000
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Class A [Member]
Common stock, authorized (in shares)	60,000,000	60,000,000
Common stock, outstanding (in shares)	43,104,231	42,503,925
Treasury stock (in shares)	12,999	10,335
Common Class B [Member]
Common stock, authorized (in shares)	20,000,000	20,000,000
Common stock, outstanding (in shares)	12,560,943	12,470,308
Treasury stock (in shares)	327,824	73,437