Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' Equity, Period Start				$ 1,323,073						$ 1,251,582	$ 1,323,073	$ 1,251,582	$ 1,146,206
Net income	75,609	80,560	69,079	53,437	56,230	[1]	104,909	[2]	56,454	58,412	278,685	276,005	217,586
Dividends											(208,286)	(186,828)	(164,514)
Issuance of shares under incentive stock plans											25,495	13,451	26,314
Share-based compensation											15,116	16,181	15,223
Excess tax benefit on stock-based compensation											7,635	5,681	5,411
Repurchase of common shares											(7,783)	(7,909)	(6,028)
Net gain (loss) from pension and postretirement plans											(496)	(46,263)	6,385
Foreign currency translation adjustment											4,352	3,546	4,162
Joint venture cash flow hedges											213	(2,373)	837
Shareholders' Equity, Period End	1,438,004				1,323,073						1,438,004	1,323,073	1,251,582
Dividends per share											$ 1.68	$ 1.52	$ 1.36
Dividends [Abstract]
Caiptal gain											$ 1.68	$ 1.52	$ 1.36
Non-taxable return of capital											$ 0.00	$ 0.00	$ 0.00
Total cash dividend per common share											$ 1.68	$ 1.52	$ 1.36
Common Shares
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' Equity, Period Start				630,286						602,882	630,286	602,882	561,962
Shares Issued, Period Start				122,035,177						121,023,140	122,035,177	121,023,140	119,312,961
Issuance of shares under incentive stock plans											25,495	13,451	26,314
Issuance of shares under incentive stock plans, Shares											1,467,024	1,220,731	1,914,341
Share-based compensation											15,116	16,181	15,223
Excess tax benefit on stock-based compensation											7,635	5,681	5,411
Repurchase of common shares											(7,783)	(7,909)	(6,028)
Repurchase of common shares, Shares											(169,757)	(208,694)	(204,162)
Shares Issued, Period End	123,332,444				122,035,177						123,332,444	122,035,177	121,023,140
Shareholders' Equity, Period End	670,749				630,286						670,749	630,286	602,882
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' Equity, Period Start				806,235						717,058	806,235	717,058	663,986
Net income											278,685	276,005	217,586
Dividends											(208,286)	(186,828)	(164,514)
Shareholders' Equity, Period End	876,634				806,235						876,634	806,235	717,058
Accumulated Other Comprehensive Income/(Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' Equity, Period Start				(113,448)						(68,358)	(113,448)	(68,358)	(79,742)
Net gain (loss) from pension and postretirement plans											(496)	(46,263)	6,385
Foreign currency translation adjustment											4,352	3,546	4,162
Joint venture cash flow hedges											213	(2,373)	837
Shareholders' Equity, Period End	$ (109,379)				$ (113,448)						$ (109,379)	$ (113,448)	$ (68,358)

[1] Fourth quarter 2011 included a pre-tax expense of $6.5 million ($4.1 million after tax) due to an increase in a disposition reserve.

[2] Third quarter 2011 included a benefit of $16.0 million from the reversal of a reserve related to the taxability of the AFMC.