Debt (Details)	1 Months Ended		2 Months Ended	3 Months Ended			9 Months Ended
	Feb. 28, 2015 USD ($)	Nov. 30, 2014 $ / shares shares	Oct. 31, 2015 USD ($)	Sep. 30, 2015 USD ($) shares	Mar. 31, 2015 USD ($) shares	Sep. 30, 2014 USD ($) shares	Sep. 30, 2015 USD ($) shares	Sep. 30, 2014 USD ($) shares	Dec. 31, 2014 USD ($) shares	Oct. 31, 2011 USD ($)
Debt Conversion							$ 146,000,000	$ 61,100,000
Debt Instrument, Face Amount				$ 33,100,000			33,100,000			$ 400,000,000
Repayments of convertible senior notes							$ (146,007,000)	$ (61,125,000)
Stock issued during period conversion of convertible notes | shares							1,419,287	521,876
Gains (Losses) on Extinguishment of Debt				$ 21,000		$ 0	$ 16,927,000	$ 10,787,000
Treasury Stock, Shares | shares				3,437,000			3,437,000		2,017,732
Treasury Stock, Value				$ 288,777,000			$ 288,777,000		$ 169,530,000
Payments in connection with deduction of outstanding warrants							(523,487,000)	$ (143,041,000)
Credit Facility [Domain]
Line of Credit Facility, Maximum Borrowing Capacity					$ 750,000,000
Line of Credit Facility, Expiration Period					5 years
Line of Credit Facility, Increase (Decrease), Net					$ 250,000,000
Line of Credit Facility, Current Borrowing Capacity				100,000,000			100,000,000
Line of Credit Facility, Fair Value of Amount Outstanding				$ 0			$ 0
Convertible senior notes
Treasury Stock, Shares | shares				1,419,268		521,876	1,419,268	521,876
Treasury Stock, Value				$ 119,200,000		$ 43,800,000	$ 119,200,000	$ 43,800,000
Additional Paid-in Capital [Member]
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments							705,900,000	156,700,000
Adjustments to Additional Paid in Capital, Warrant Issued					$ 23,300,000
Scenario, Forecast [Member]
Debt Conversion Not Yet Settled			$ 20,500,000
Warrant Transactions [Member]
Maximum reduction of warrants held by warrant holder | shares		493,229
Limit price per share for warrant holders to close out hedge position | $ / shares		$ 397.75
Accounts Payable, Other									$ 59,800,000
Payments in connection with deduction of outstanding warrants	$ (124,000,000)						$ (399,500,000)	$ (143,041,000)
Reduction of number of warrants | shares					416,480		898,547.000	727,516
Weighted Average Number of Shares Outstanding, Basic | shares							2,225,068
Subsequent Event [Member] | Convertible senior notes
Trading days to calculate settlement			40