Incentive Plans (Details Textual) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Incentive Plans (Textual)
Pretax compensation expense	$ 17,537	$ 19,746	$ 21,861
Maximum number of shares that may be issued under the 2006 Omnibus Long-term Incentive Plan	11,900,000
Additional number of shares that may be issued under the 2006 Omnibus Long-term Incentive Plan	6,500,000
Expense provision under cash-based compensation plans	6,938	5,080	1,954
Performance Shares [Member]
Incentive Plans (Textual)
Number of common stock per unit entitled upon vesting	1
Percentage of payment based upon Total Shareholder Return performance prior to 2010	50.00%
Percentage of payment based upon achievement of established internal financial performance targets prior to 2010	50.00%
Share based compensation plans vesting period (in years)	4 years	3 years
Pretax compensation expense	$ 8,879	$ 7,562	$ 5,350
Weighted-average Grant Date Fair Value, Granted	$ 39.38	$ 40.34	$ 45.72
Performance Shares [Member] | Minimum [Member]
Incentive Plans (Textual)
Units paid target range	0.00%
Performance Shares [Member] | Maximum [Member]
Incentive Plans (Textual)
Units paid target range	200.00%
Stock Options/SOSARs [Member]
Incentive Plans (Textual)
Award expiration date for share-based compensation plans	10 years subsequent to the grant
Stock Options/SOSARs [Member] | Minimum [Member]
Incentive Plans (Textual)
Share based compensation plans vesting period (in years)	3 years
Stock Options/SOSARs [Member] | Maximum [Member]
Incentive Plans (Textual)
Share based compensation plans vesting period (in years)	5 years