Note 5 - Capital Stock (Details Textual) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended	12 Months Ended
	Jan. 22, 2020	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Preferred Stock, Shares Outstanding, Ending Balance		0	0	0
Common Stock, Dividends, Per Share, Declared		$ 0.26	$ 1.04	$ 0.96	$ 0.92
Treasury Stock, Shares, Acquired			2,800
Treasury Stock, Value, Acquired, Cost Method			$ 275,657	$ 150,338	$ 179,813
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 95,000	$ 95,000
Exercise or Vesting [Member]
Common Stock, Capital Shares Reserved for Future Issuance		1,700	1,700
Future Issuance [Member]
Common Stock, Capital Shares Reserved for Future Issuance		5,700	5,700
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.27
Stock Repurchase Program, Authorized Amount	$ 500,000
Dividends Payable, Date to be Paid	Feb. 21, 2020
Dividends Payable, Date of Record	Feb. 07, 2020