Indebtedness And Borrowing Facilities (2013 Convertible Notes) (Details) (USD $)	1 Months Ended	3 Months Ended				12 Months Ended			1 Months Ended	3 Months Ended	12 Months Ended
	Sep. 30, 2009	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Aug. 31, 2008 Five Year 2.5% Unsecured Convertible Notes Due In 2013 [Member] item	Sep. 30, 2012 Five Year 2.5% Unsecured Convertible Notes Due In 2013 [Member]	Dec. 31, 2012 Five Year 2.5% Unsecured Convertible Notes Due In 2013 [Member] item	Dec. 31, 2011 Five Year 2.5% Unsecured Convertible Notes Due In 2013 [Member]	Dec. 31, 2010 Five Year 2.5% Unsecured Convertible Notes Due In 2013 [Member]	Dec. 31, 2009 Five Year 2.5% Unsecured Convertible Notes Due In 2013 [Member]	Dec. 31, 2008 Five Year 2.5% Unsecured Convertible Notes Due In 2013 [Member]
Debt Instrument [Line Items]
Debt instrument face amount						$ 787,900,000	$ 701,000,000		$ 375,000,000		$ 286,900,000	$ 375,000,000
Maturity date									Aug. 01, 2013
Interest rate of debt instrument									2.50%		2.50%
Interest payable terms									semiannually, in arrears, on February 1 and August 1
Principal amounts for conversion									1,000		1,000	1,000
Conversion rate									41.2414		42.0746
Conversion price						$ 23.77	$ 23.77	$ 24.25	$ 24.25
Conversion, start date									May 01, 2013
Conversion, end date									Jul. 29, 2013
Trading days									at least 20 trading days in the period of 30 consecutive trading days
Convertible note conversion trigger stock price as a percentage of conversion price									130.00%
Measurement period									five consecutive business days immediately after any 10 consecutive trading day period
Convertible note conversion trigger note trading price as a percentage of implied equity value									98.00%
Dividends paid			$ 0.125	$ 0.125			$ 0.50	$ 0.25
Debt conversion ratio									41.2414		42.0746
Convertible notes would result in issuance common stock shares									15,500,000		15,800,000
Dividends per share, increase from previous period							$ 0.25
Percentage of principal amount to be paid to repurchase convertible notes upon change in control									100.00%
Convertible notes effective conversion price											$ 35.88
Percent of effective conversion premium over conversion price											100.00%
Equity component of convertible notes									73,000,000
Annual interest rate calculated for similar debt instrument									7.60%
Carrying value of convertible notes											278,700,000	346,900,000
Interest paid at coupon rate											8,700,000	9,400,000	9,400,000	9,400,000
Recognized non-cash interest expense						16,300,000	16,300,000	15,000,000			16,000,000	16,100,000	15,000,000
Payments of debt issuance costs						7,300,000	7,100,000								7,500,000
Unamortized debt issuance costs											400,000
Debt issuance costs related to equity component															1,900,000
Amount of debt repurchased										88,100,000
Amount paid for debt										84,800,000
Principal amount of long-term debt repayments	43,200,000					88,100,000	306,800,000			84,600,000
Loss on extinguishment on debt		(600,000)			(4,100,000)	(600,000)	(4,100,000)			600,000
Accrued and unpaid interest										200,000
Aggregate amount of debt outstanding											$ 286,900,000