Share-Based Payments (Details 9) (Performance vested restricted stock units [Member], USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Performance vested restricted stock units [Member]
Performance-Vested Restricted Stock Units (PVRSUs)
Beginning Balance, Unvested, Shares	154,000
Beginning Balance, Weighted Average Grant Date Fair Value	$ 49.24
Shares, Granted	1,000	4,000	325,000
Weighted Average Grant Date Fair Value, Granted	$ 53.64	$ 53.64	$ 49.42
Shares, Vested	(75,000)
Weighted Average Grant Date Fair Value, Vested	$ 49.51
Shares, Forfeited	(33,000)
Weighted Average Grant Date Fair Value, Forfeited	$ 48.61
Ending Balance, Unvested, Shares	47,000	154,000
Ending Balance, Weighted Average Grant Date Fair Value	$ 49.34	$ 49.24