Shareholders' Equity (Summary of Restricted Stock and Goal-Based Stock Activity) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Restricted Stock [Member]
Nonvested beginning, Shares	1,476	1,484	1,756
Granted, Shares	299	463	533
Vested, Shares	(617)	(618)	(913)
Cancelled and forfeited, Shares	(25)	(39)	(77)
Converted from goal-based stock to restricted stock, Shares	(168)	(186)	(185)
Nonvested ending, Shares	1,301	1,476	1,484
Nonvested beginning, Weighted Average Grant Date Fair Value	$ 38.20	$ 39.88	$ 38.55
Granted, Weighted Average Grant Date Fair Value	$ 43.68	$ 38.80	$ 33.84
Vested, Weighted Average Grant Date Fair Value	$ 40.72	$ 43.54	$ 34.81
Cancelled and forfeited, Weighted Average Grant Date Fair Value	$ 36.29	$ 36.92	$ 38.32
Converted from goal-based stock to restricted stock, Weighted Average Grant Date Fair Value	$ 30.99	$ 40.84	$ 44.18
Nonvested ending, Weighted Average Grant Date Fair Value	$ 37.37	$ 38.20	$ 39.88
Goal-Based Stock [Member]
Nonvested beginning, Shares	161	323	315
Granted, Shares	3	9	165
Vested, Shares	(20)	(16)	(28)
Cancelled and forfeited, Shares	0	(8)	(2)
Converted from goal-based stock to restricted stock, Shares	(132)	(147)	(127)
Nonvested ending, Shares	12	161	323
Nonvested beginning, Weighted Average Grant Date Fair Value	$ 31.79	$ 36.12	$ 42.56
Granted, Weighted Average Grant Date Fair Value	$ 43.54	$ 37.46	$ 31.43
Vested, Weighted Average Grant Date Fair Value	$ 34.62	$ 39.31	$ 44.38
Cancelled and forfeited, Weighted Average Grant Date Fair Value	$ 0.00	$ 30.99	$ 37.24
Converted from goal-based stock to restricted stock, Weighted Average Grant Date Fair Value	$ 30.99	$ 40.84	$ 44.18
Nonvested ending, Weighted Average Grant Date Fair Value	$ 39.19	$ 31.79	$ 36.12