Debt (Details) - USD ($)	1 Months Ended				3 Months Ended				12 Months Ended
	Nov. 30, 2015	Feb. 28, 2015	Nov. 30, 2014	Oct. 31, 2011	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Reclassification of warrants			493,229
Treasury Stock, Value					$ 316,240,000		$ 306,069,000		$ 316,240,000	$ 306,069,000
Net carrying amount of the liability component [Abstract]
Treasury Stock, Shares					3,763,868		3,642,820		3,763,868	3,642,820
Warrants [Abstract]
Adjustments to Additional Paid in Capital, Other									$ (643,365,000)	$ (449,456,000)	$ (294,552,000)
Payments for Repurchase of Warrants									643,365,000	573,487,000	294,552,000
Maximum amount of warrant payable										(23,317,000)	148,496,000
Maximum share price for warrant holders to close out hedge position	$ 535.00
Convertible Debt [Abstract]
Repayments of Convertible Debt									$ 12,894,000	$ 166,467,000	220,639,000
Stock Issued During Period, Shares, New Issues									121,058	1,625,113
Loss on Extinguishment of Debt										$ 18,861,000
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments									$ 47,789,000	819,657,000	691,869,000
Line of Credit Facility [Abstract]
Treasury Stock, Value, Acquired, Cost Method									0	$ 0	$ 0
November 2016 Agreement [Member] [Member]
Warrants [Abstract]
Payments for Repurchase of Warrants					$ 401,200,000
Warrant
Warrants [Abstract]
Strike price of the warrant transaction (in dollars per share)				$ 103.41
Proceeds received from the Warrant				$ 93,800,000
Reduction of number of warrants		416,480				360,406	115,970			898,547	1,220,745
Payments for Repurchase of Warrants		$ 124,000,000				$ 135,300,000	$ 50,000,000			$ 399,500,000	$ 294,600,000
Accounts Payable, Other											59,800,000
Liabilities, Fair Value Adjustment					$ 0		$ 0		$ 0	$ 0	87,500,000
February 2016 Agreement [Member]
Warrants [Abstract]
Reduction of number of warrants									403,665
Payments for Repurchase of Warrants									$ 106,900,000
Maximum reduction of warrants held by warrant holder									975,142
Maximum share price for warrant holders to close out hedge position									$ 375.00
Call option
Convertible Debt [Abstract]
Purchase of convertible note hedges				117,500,000
Convertible senior notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount				$ 400,000,000.0
Interest rate, stated percentage				1.875%			1.875%			1.875%
Initial conversion price (in dollars per share)				$ 84.02
Estimated fair value of the liability component				$ 271,100,000
Carrying amount of equity component				120,900,000
Gross proceeds from the issuance of the Notes				$ 392,000,000
Effective interest rate used to amortize the discount on the liability component					10.20%				10.20%
Net carrying amount of the liability component [Abstract]
Convertible Debt					$ 0		$ 11,154,000		$ 0	$ 11,154,000
Unamortized discount					0		(352,000)		0	(352,000)
Convertible Notes Payable					0		$ 10,802,000		0	10,802,000
Interest Expense, Debt [Abstract]
Contractual coupon interest rate									7,000	544,000	5,036,000
Amortization of discount and note issuance costs									150,000	2,818,000	17,821,000
Total interest expense									157,000	3,362,000	22,857,000
Credit Facility [Domain]
Line of Credit Facility [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity								$ 750,000,000
Line of Credit Facility, Expiration Period								5 years
Available increase to the credit facility								$ 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
Additional Paid-in Capital
Warrants [Abstract]
Adjustments to Additional Paid in Capital, Other								$ 23,300,000	(643,365,000)	(449,456,000)	(294,552,000)
Maximum amount of warrant payable										(23,317,000)	148,496,000
Convertible Debt [Abstract]
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments									47,789,000	819,657,000	691,869,000
Line of Credit Facility [Abstract]
Treasury Stock, Value, Acquired, Cost Method									10,171,000	136,539,000	169,530,000
Treasury Stock
Line of Credit Facility [Abstract]
Treasury Stock, Value, Acquired, Cost Method									$ (10,171,000)	$ (136,539,000)	$ (169,530,000)
Treasury Stock, Shares, Acquired									121,048	1,625,088	2,018,000