Corporate Debt - Additional Information (Details) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 31, 2012
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	6.98%	6.50%	6.98%
Gains (Losses) on Extinguishment of Debt	$ (12,500,000)	$ 0	$ 12,489,000	$ 48,579,000
Repayments of Long-term Debt		17,220,000	362,931,000	75,292,000
Deferred Tax Liabilities Debt Discount On Convertible Notes				33,000,000
Equity portion of Convertible Notes, net of issuance costs				48,697,000
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs				2,700,000
Convertible Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount				290,000,000.0
Debt Issuance Cost				6,800,000
Debt Instrument Original Issue Discount				84,500,000
Interest Expense, Debt		23,400,000	22,400,000	4,200,000
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date			Dec. 15, 2021
Term Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		1,500,000,000
Corporate debt	1,477,044,000	1,464,978,000	1,477,044,000
Weighted Average Stated Interest Rate	4.75%	4.75%	4.75%
Debt Instrument, Maturity Date		Dec. 18, 2020
Term Loan [Member] | Two Thousand Twelve Term Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount				700,000,000
Term Loan [Member] | Incremental Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	1,075,000,000		1,075,000,000
Other General and Administrative Expense			6,400,000
Debt Issuance Cost			5,400,000
Term Loan [Member] | TwoThousandThirteenTermLoan [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	1,500,000,000.0		1,500,000,000.0
Term Loan [Member] | Second Lien Term Loan Member [Member]
Debt Instrument [Line Items]
Gains (Losses) on Extinguishment of Debt				(43,400,000)
Repayments of Long-term Debt				265,000,000
Corporate Debt Securities [Member] | Two Thousand Twelve Term Loan [Member]
Debt Instrument [Line Items]
Gains (Losses) on Extinguishment of Debt			12,500,000
Corporate Debt Securities [Member] | First Lien Term Loan [Member]
Debt Instrument [Line Items]
Gains (Losses) on Extinguishment of Debt				5,200,000
Senior Notes [Member]
Debt Instrument [Line Items]
Corporate debt	575,000,000	575,000,000	575,000,000
Weighted Average Stated Interest Rate	7.875%	7.875%	7.875%
Proceeds from Issuance of Debt			561,300,000
Debt Instrument, Interest Rate, Stated Percentage		7.875%
Convertible Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	10.60%	10.60%	10.60%	10.60%
Debt Instrument, Face Amount					290,000,000
Debt Instrument, Unamortized Discount	74,100,000	64,300,000	74,100,000
Corporate debt	215,935,000	225,690,000	215,935,000
Weighted Average Stated Interest Rate	4.50%	4.50%	4.50%
Debt Instrument, Maturity Date				Nov. 01, 2019
Debt Instrument, Convertible, Conversion Ratio		17.0068
Debt Instrument, Interest Rate, Stated Percentage					4.50%
Debt Instrument, Convertible, Conversion Price		$ 58.80
Debt Conversion Premium Percentage		40.00%
Shares Issued, Price Per Share		$ 42.00
Proceeds from Convertible Debt				280,400,000
Amortization of Debt Discount (Premium)		9,800,000	8,800,000	1,600,000
Debt Instrument, Convertible, Remaining Discount Amortization Period		4 years 9 months 18 days
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		125,000,000
Debt Instrument, Unamortized Discount	23,000,000		23,000,000
Line of Credit Facility, Fair Value of Amount Outstanding		0
Long-term Line of Credit		300,000
Line of Credit Facility, Remaining Borrowing Capacity		124,700,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.50%
Debt Instrument, Maturity Date		Dec. 19, 2018
Revolving Credit Facility [Member] | 2013 Revolver [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	125,000,000		125,000,000
Revolving Credit Facility [Member] | 2012 Revolver [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				125,000,000
Line of Credit [Member] | 2013 Revolver [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 25,000,000		$ 25,000,000