Debt Convertible Debentures (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Feb. 06, 2013
Debt Instrument [Line Items]
Redemption Price Of Debt As Percentage Of The Principal Amount Of The Debentures upon change in control and credit rating decline	101.00%
Long-term Debt, Gross	$ 732,500,000
Convertible Debt [Member]
Debt Instrument [Line Items]
Redemption Price Of Debt As Percentage Of The Principal Amount Of The Debentures upon change in control and credit rating decline	100.00%
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Aggregate Principal Outstanding Of Convertible Junior Subordinated Debentures	732,500,000
Debt Instrument Periodic Payment Interest Rate	4.75%
Events Triggering Payment Of Deferred Interest On Debentures	After five years of deferral at the Company’s option, or upon the occurrence of a mandatory trigger event
Conversation Of Debt Maximum Deferral Period	10
Convertible Debt Condition One For Debt Conversion	140.00%
Current conversion price of debentures per share	$ 81.13
Debt Instrument Convertible Conversion Rate Per Share				$ 17.2563
Current Conversion Amount Per Principal Amount Of Debentures				1,000
Adjusted Conversion Price Of Debentures Per Share				$ 57.95
Period of redemption of debentures	at least 20 out of the 30 consecutive trading days immediately prior to the date on which notice of redemption is given
Convertible Debt Conversion Period Description	130.00%
Debt Instrument, Convertible, Conversion Price	$ 75.34
Maximum Percentage Of The Company's Net Cash Proceeds From The Sale Of Its Common Stock And Rights To Acquire Common Stock Which Can Be Used For Repayment Of Debt	400.00%
Debt Instrument, Convertible, Carrying Amount of Equity Component	215,400,000	215,400,000
Long-term Debt, Gross	732,500,000	732,500,000
Debt Instrument, Unamortized Discount	355,100,000	357,300,000
Convertible Subordinated Debt	377,400,000	375,200,000
Debt Instrument, Convertible, Effective Interest Rate	4.90%	4.90%	4.90%
Interest Expense, Debt	34,800,000	34,800,000	34,800,000
Amortization of Debt Discount (Premium)	2,100,000	1,800,000	1,600,000
Debt Instrument, Convertible, Remaining Discount Amortization Period	29
Senior Notes Four Member
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.875%
Minimum amount of revolving credit facility increase, upon request	$ 250,000,000
Minimum [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Number Of Days Percentage Closing Common Stock Price Exceeds Conversion Price Condition To Convert Debentures	20
Maximum [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Number Of Days Percentage Closing Common Stock Price Exceeds Conversion Price Condition To Convert Debentures	30