Shareholder's Equity (Schedule of Stock Option Activity (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Shareholders' Equity
Outstanding at beginning of period, Number of Shares	1,662,830	2,510,054	2,901,989
Options exercised, Number of Shares	(1,392,366)	(841,599)	(374,350)
Options terminated, Number of Shares		(5,625)	(17,585)
Outstanding at end of period, Number of Shares	270,464	1,662,830	2,510,054	2,901,989
Vested or expected to vest at end of period, Number of Shares	270,464
Exercisable at end of period, Number of Shares	270,464
Outstanding at beginning of period, Weighted Average Exercise Price	$ 23.82	$ 23.09	$ 22.49
Options exercised, Weighted Average Grant Price	$ 23.95	$ 21.64	$ 18.36
Options terminated, Weighted Average Grant Price		$ 21.85	$ 25.42
Outstanding at end of period, Weighted Average Exercise Price	$ 23.16	$ 23.82	$ 23.09	$ 22.49
Vested or expected to vest at end of period, Weighted Average Exercise Price price	$ 23.16
Exercisable at end of period, Weighted Average Exercise Price	$ 23.16
Weighted Average Remaining Contractual Term, Period Start	2 years 6 months 0 days	2 years 10 months 24 days	3 years 4 months 24 days	4 years 6 months 0 days
Weighted Average Remaining Contractual Term, Period End	2 years 6 months 0 days	2 years 10 months 24 days	3 years 4 months 24 days	4 years 6 months 0 days
Weighted Average Remaining Contractual Term, Vested or expected to vest	2 years 6 months 0 days
Weighted Average Remaining Contractual Term, Exercisable	2 years 6 months 0 days