Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' Equity, Period Start			$ 1,323,073	$ 1,251,582	$ 1,251,582
Net Income	80,560	104,909	203,076	219,774	276,005
Dividends			(153,545)		(186,828)
Issuance of shares under incentive stock plans			20,732		13,451
Stock-based compensation			12,212		16,181
Excess tax benefit on stock-based compensation			7,057		5,681
Repurchase of common shares			(7,783)		(7,909)
Net loss from pension and postretirement plans	3,401	2,261	9,943	6,449	(46,263)
Foreign currency translation adjustment	5,373	3,584	3,115	11,314	3,546
New Zealand joint venture cash flow hedges	878	(630)	86	(498)	(2,373)
Shareholders' Equity, Period End	1,417,966		1,417,966		1,323,073
Dividends [Abstract]
Dividends per share	$ 0.44	$ 0.40	$ 1.24	$ 1.12	$ 1.52
Common Shares [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' Equity, Period Start			630,286	602,882	602,882
Shares Issued, Period Start			122,035,177	121,023,140	121,023,140
Issuance of shares under incentive stock plans			20,732		13,451
Issuance of shares under incentive stock plan, Shares			1,323,581		1,220,731
Stock-based compensation			12,212		16,181
Excess tax benefit on stock-based compensation			7,057		5,681
Repurchase of common shares			(7,783)		(7,909)
Repurchase of common shares, Shares			(169,757)		(208,694)
Shares Issued, Period End	123,189,001		123,189,001		122,035,177
Shareholders' Equity, Period End	662,504		662,504		630,286
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' Equity, Period Start			806,235	717,058	717,058
Net Income			203,076		276,005
Dividends			(153,545)		(186,828)
Shareholders' Equity, Period End	855,766		855,766		806,235
Accumulated Other Comprehensive Loss [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' Equity, Period Start			(113,448)	(68,358)	(68,358)
Net loss from pension and postretirement plans			9,943		(46,263)
Foreign currency translation adjustment			3,115		3,546
New Zealand joint venture cash flow hedges			86		(2,373)
Shareholders' Equity, Period End	$ (100,304)		$ (100,304)		$ (113,448)