Debt (Details)	1 Months Ended			3 Months Ended
	Apr. 30, 2016 USD ($)	Feb. 28, 2015 USD ($)	Nov. 30, 2014 $ / shares	Mar. 31, 2016 USD ($) $ / shares shares	Mar. 31, 2015 USD ($) shares	Dec. 31, 2015 USD ($) shares
Debt Conversion				$ 1,700,000	$ 16,700,000
Repayments of convertible senior notes				$ (1,739,000)	$ (16,686,000)
Stock Issued During Period, Shares, New Issues | shares				16,774	146,253
Treasury Stock, Shares | shares				3,659,588		3,642,820
Treasury Stock, Value				$ 307,478,000		$ 306,069,000
Limit price per share for warrant holders to close out hedge position | $ / shares			$ 397.75
Payments in connection with deduction of outstanding warrants		$ (124,000,000)		(242,117,000)	$ (124,531,000)
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, Fair Value of Amount Outstanding				$ 0
Convertible senior notes
Treasury Stock, Shares | shares				16,768	146,248
Treasury Stock, Value				$ 1,400,000	$ 12,300,000
Convertible Debt				10,600,000		$ 11,200,000
Additional Paid-in Capital [Member]
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments				$ 6,700,000	62,600,000
Adjustments to Additional Paid in Capital, Warrant Issued					$ 23,300,000
Scenario, Forecast [Member]
Debt Conversion Not Yet Settled	$ 10,400,000
Warrant Transactions [Member]
Reduction of number of warrants | shares					416,480
Warrant outstanding balance | shares				1,345,027
November 2015 Warrant Agreement
Limit price per share for warrant holders to close out hedge position | $ / shares				$ 535.00
Payments in connection with deduction of outstanding warrants				$ 135,200,000
Reduction of number of warrants | shares				360,406
February 2016 Warrant Agreement
Maximum reduction of warrants held by warrant holder | shares				975,142
Limit price per share for warrant holders to close out hedge position | $ / shares				$ 375.00
Payments in connection with deduction of outstanding warrants				$ 106,900,000
Reduction of number of warrants | shares				403,665
Subsequent Event [Member] | Convertible senior notes
Trading days to calculate settlement	40