Shareholders' Equity (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended			3 Months Ended			12 Months Ended		3 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Interim Cash Dividends [Member]	Jun. 30, 2012 Interim Cash Dividends [Member]	Dec. 31, 2012 Final Cash Dividends [Member]	Dec. 31, 2012 Minimum [Member]	Dec. 31, 2012 Maximum [Member]	Dec. 31, 2012 2007 Plan [Member] plans	Dec. 31, 2012 1998 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of active equity compensation plans										1
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	2,569,000	2,569,000								20,000,000	0
Vesting Rate When Specified Diluted Earnings Per Share Targets are Achieved										50.00%
Vesting Rate Higher Specified Diluted Earnings Per Share Targets are Achieved										50.00%
Stock options granted prior to 2006, vesting period, years		7 years
Option pricing model used to determine fair value of stock options		Black-Scholes
Weighted average fair value of stock options granted		$ 6.73	$ 5.70	$ 9.65
Change in management estimate of stock based compensation expense amortization				$ 11,663,000
Previously recognized stock-based compensation costs reversed				6,375,000
Unrecognized compensation cost	50,264,000	50,264,000		27,460,000
Total options that were exercisable	9,760,000	9,760,000	11,680,000	14,247,000
Expiration date for options outstanding								Dec. 16, 2013	Dec. 11, 2022
Options outstanding weighted average remaining contractual life, years		5 years 10 months 24 days
Total intrinsic value of options exercised		19,565,000	8,642,000
Aggregate intrinsic value of options exercisable	51,087,000	51,087,000
Total intrinsic value of options outstanding	64,823,000	64,823,000
Share Price	$ 23.34	$ 23.34
Employee stock purchase plan, employee eligible percentage on offerings of common stock		85.00%
Shares reserved under the plan	15,600,000	15,600,000
Issuance of common stock under the employee stock purchase plan, shares		11,580,000
Employee Stock Ownership Plan (ESOP), Compensation Expense		0	0	0
Remaining stock repurchase authorization amount	91,012,000
Rights received by common shareholder for each common share outstanding, rights	1	1
Series A Junior Participating Preferred stock, par value	$ 0.05	$ 0.05	$ 0.05
Securities and assets of equivalent value, purchase price, per unit	$ 150.00	$ 150.00
Number of days, rights become exercisable following public announcement		10
Acquiring Person, beneficial ownership of the outstanding common stock, minimum percentage	20.00%	20.00%
Holders, other than an acquiring person, right to purchase of common stock upon exercise of rights		twice
Common shares received by holders upon surrender of rights, percentage		50.00%
Rights non-voting, redeemable days		0 years 0 months 10 days
Right redeemable price, per right	$ 0.01	$ 0.01
Common Stock, Dividends, Per Share, Declared		$ 0.63	$ 0.27	$ 0.20	$ 0.16	$ 0.15	$ 0.32
Dividends, Common Stock		$ 108,817,000	$ 48,558,000	$ 37,513,000