Note 9 - Dividends (Details Textual) - USD ($) $ / shares in Units, $ in Thousands					1 Months Ended		3 Months Ended							12 Months Ended
	Dec. 31, 2021	Oct. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Aug. 31, 2021	Nov. 30, 2020	Aug. 31, 2019
Payments of Ordinary Dividends, Common Stock														$ 54,735	$ 52,366	$ 42,089
Line Of Credit Facility Dividend Restrictions Percentage Of Net Income Limit	25.00%													25.00%				25.00%
Line of Credit Facility, Waiver to Pay Dividends, Maximum	$ 80,000													$ 80,000			$ 80,000	$ 60,000	$ 65,000
Special Dividend [Member]
Payments of Ordinary Dividends, Common Stock														$ 54,700
Common Stock, Dividends, Per Share, Declared (in dollars per share)		$ 0.50				$ 0.433
Paid Quarterly [Member]
Payments of Ordinary Dividends, Common Stock															$ 52,400
Common Stock, Dividends, Per Share, Declared (in dollars per share)	$ 0.04	$ 0.04	$ 0.04	$ 0.04	$ 0.50		$ 0.04	$ 0.027	$ 0.027	$ 0.02	$ 0.02	$ 0.02	$ 0.02