Note 5 - Capital Stock (Details Textual) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		3 Months Ended	12 Months Ended
	Jan. 24, 2018	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Preferred Stock, Shares Outstanding		0	0	0
Common Stock, Dividends, Per Share, Cash Paid		$ 0.23
Common Stock, Dividends, Per Share, Declared			$ 0.92	$ 0.88	$ 0.84
Treasury Stock, Shares, Acquired			1,900
Treasury Stock, Value, Acquired, Cost Method			$ 179.8
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 521.4	$ 521.4
Exercise or Vesting [Member]
Common Stock, Capital Shares Reserved for Future Issuance		1,600	1,600
Future Issuance [Member]
Common Stock, Capital Shares Reserved for Future Issuance		6,800	6,800
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.24
Dividends Payable, Date Declared	Jan. 24, 2018
Dividends Payable, Date to be Paid	Feb. 23, 2018
Dividends Payable, Date of Record	Feb. 09, 2018