Note 6 - Capital Stock (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Apr. 23, 2020	Jan. 22, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Apr. 20, 2017
Stock Repurchase Program, Authorized Amount		$ 500,000				$ 500,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount			$ 520,000
Treasury Stock, Shares, Acquired (in shares)			800,000
Treasury Stock, Value, Acquired, Cost Method			$ 75,193
Common Stock, Dividends, Per Share, Declared (in dollars per share)		$ 0.27	$ 0.27	$ 0.26	$ 0.26
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared (in dollars per share)	$ 0.27
Dividends Payable, Date Declared	Apr. 23, 2020
Dividends Payable, Date to be Paid	May 22, 2020
Dividends Payable, Date of Record	May 08, 2020