Note 5 - Capital Stock (Details Textual) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	12 Months Ended
	Jan. 21, 2021	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Preferred Stock, Shares Outstanding, Ending Balance (in shares)		0	0	0
Common Stock, Dividends, Per Share, Declared (in dollars per share)		$ 0.27	$ 1.08	$ 1.04	$ 0.96
Treasury Stock, Shares, Acquired (in shares)			942,000
Treasury Stock, Value, Acquired, Cost Method			$ 92,548	$ 275,657	$ 150,338
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 503,000	$ 503,000
Exercise or Vesting [Member]
Common Stock, Capital Shares Reserved for Future Issuance (in shares)		1,700,000	1,700,000
Future Issuance [Member]
Common Stock, Capital Shares Reserved for Future Issuance (in shares)		5,100,000	5,100,000
Subsequent Event [Member]
Dividends Payable, Date Declared	Jan. 21, 2021
Common Stock, Dividends, Per Share, Declared (in dollars per share)	$ 0.28
Dividends Payable, Date to be Paid	Feb. 19, 2021
Dividends Payable, Date of Record	Feb. 05, 2021