Note 6 - Stockholders' Equity (Details Textual) $ / shares in Units, $ in Thousands		3 Months Ended						9 Months Ended
	Feb. 24, 2021 $ / shares	Sep. 30, 2021 USD ($) $ / shares shares	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($) $ / shares	Dec. 31, 2020 shares
Capital Units, Authorized (in shares)		245,000,000						245,000,000
Common Stock, Shares Authorized (in shares)		200,000,000						200,000,000		200,000,000
Preferred Stock, Shares Authorized (in shares)		20,000,000						20,000,000
Common Stock, Voting Rights, Votes Per Share		1						1
Common Stock, Dividends, Per Share, Declared (in dollars per share) | $ / shares		$ 0.08			$ 0			$ 0.24	$ 0
Dividends, Common Stock, Total | $		$ 8,000	$ 7,000	$ 8,000
Common Stock, Capital Shares Reserved for Future Issuance (in shares)		3,209,452						3,209,452		4,006,948
Treasury Stock, Value, Acquired, Cost Method | $					$ 10,000	$ 43,000	$ 6,000
Common Class A [Member]
Common Stock, Shares Authorized (in shares)		25,000,000						25,000,000		25,000,000
Common Stock, Voting Rights, Votes Per Share		10						10
Common Stock, Capital Shares Reserved for Future Issuance (in shares)		1,103,015						1,103,015		1,336,440
Common Stock and Class A Common Stock [Member]
Common Stock, Dividends, Per Share, Declared (in dollars per share) | $ / shares	$ 0.08
Dividends, Common Stock, Total | $								$ 23,000	$ 0
Treasury Stock, Value, Acquired, Cost Method | $								0
Stock Repurchase Program, Remaining Authorized Repurchase Amount | $		$ 204,000						$ 204,000