Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Long-term Debt	$ 2,346,488,000
Debt Instrument, Unamortized Discount	382,212,000	573,082,000
Long-term Debt, Gross	2,346,488,000	2,500,434,000
Debt, Current	446,717,000	527,204,000
Long-term Debt, Excluding Current Maturities	1,517,559,000	1,418,819,000
Current Fiscal Year End Date	--12-31
Interest Paid	90,000,000	88,000,000	91,000,000
Letters of Credit Outstanding, Amount	14,000,000
Senior Term Loan [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	0	398,438,000
Senior Term Loan, due 2019 [Domain]
Debt Instrument [Line Items]
Long-term Debt, Gross	395,000,000	0
Debt Instrument, Initial Face Value	400,000,000
Amortization of Financing Costs	1,000,000	1,000,000	300,000
4.00% Junior Subordinated Convertible Debentures, due 2033 [Member]
Debt Instrument [Line Items]
Long-term Debt	188,550,000	186,136,000
Debt Instrument, Unamortized Discount	118,133,000	121,017,000
Long-term Debt, Gross	306,683,000	307,153,000
Long-term Debt, Fair Value	550,200,000	455,900,000
7.75% Senior Subordinated Notes, Due 2020 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	0	400,000,000
Long-term Debt, Fair Value	0	435,800,000
Amortization of Financing Costs	1,000,000	1,000,000	1,000,000
Write off of Deferred Debt Issuance Cost	5,000,000	2,000,000
4.75% Senior Notes, due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	400,000,000	0
Long-term Debt, Fair Value	408,000,000	0
Debt Instrument, Initial Face Value	400,000,000
5.00% Senior Notes, due 2024 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	300,000,000	0
Long-term Debt, Fair Value	316,700,000	0
Debt Instrument, Initial Face Value	300,000,000
3.75% Convertible Senior Subordinated Notes, due 2025 [Member]
Debt Instrument [Line Items]
Long-term Debt	54,148,000	87,310,000
Debt Instrument, Unamortized Discount	25,824,000	45,098,000
Long-term Debt, Gross	79,972,000	132,408,000
Long-term Debt, Fair Value	211,900,000	306,500,000
Write off of Deferred Debt Issuance Cost	1,000,000	2,000,000	4,000,000
3.25% Convertible Senior Subordinated Exchange Debentures, due 2035 [Member]
Debt Instrument [Line Items]
Long-term Debt	216,738,000	0
Debt Instrument, Unamortized Discount	24,729,000	0
Long-term Debt, Gross	241,467,000	0
Long-term Debt, Fair Value	279,500,000	0
3.75% Convertible Senior Subordinated Notes Due 2042 [Member]
Debt Instrument [Line Items]
Long-term Debt	0	225,014,000
Debt Instrument, Unamortized Discount	0	164,986,000
Long-term Debt, Gross	0	390,000,000
Long-term Debt, Fair Value	0	592,800,000
Write off of Deferred Debt Issuance Cost	3,000,000
3.5% Convertible senior subordinated debt [Domain]
Debt Instrument [Line Items]
Long-term Debt, Gross	424,250,000	424,250,000
3.25% Convertible Senior Debentures, Due 2035 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	186,033,000	427,500,000
3.25% Convertible Senior Debentures, Due 2035 [Member]
Debt Instrument [Line Items]
Long-term Debt	178,284,000	393,126,000
Debt Instrument, Unamortized Discount	7,749,000	34,374,000
Long-term Debt, Gross		427,500,000
Long-term Debt, Fair Value	197,000,000	457,400,000
Amortization of Financing Costs	1,000,000
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	13,083,000	20,685,000
7.75% interest rate swap agreement - fair value hedge [Member]
Debt Instrument [Line Items]
Derivative, Fair Value, Net	0	18,671,000
2011 Senior Credit Agreement [Member]
Debt Instrument [Line Items]
Write off of Deferred Debt Issuance Cost			$ 8,000,000