Debt (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended				3 Months Ended			12 Months Ended
	Nov. 30, 2015	Feb. 28, 2015	Nov. 30, 2014	Oct. 31, 2011	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Treasury Stock, Value						$ 306,069		$ 306,069	$ 169,530
Net carrying amount of the liability component [Abstract]
Treasury Stock, Shares						3,642,820		3,642,820	2,017,732
Warrants [Abstract]
Adjustments to Additional Paid in Capital, Other								$ (449,456)	$ (294,552)
Payments for Repurchase of Warrants								573,487	294,552	$ 0
Maximum reduction of warrants held by warrant holder	476,376		493,229
Fair Value Adjustment of Warrants									1,200
Maximum amount of warrant payable								23,317	148,496
Maximum share price for warrant holders to close out hedge position	$ 535.00		$ 397.75
Convertible Debt [Abstract]
Debt Conversion									230,600
Repayments of Convertible Debt								$ 166,467	$ 220,639	0
Stock Issued During Period, Shares, New Issues								1,625,113	2,017,732
Loss on Extinguishment of Debt								$ 18,861	$ 33,469	0
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments								$ 819,657	$ 691,869
Warrant
Warrants [Abstract]
Strike price of the warrant transaction (in dollars per share)				$ 103.41
Proceeds received from the Warrant				$ 93,800
Reduction of number of warrants						115,970	416,480	898,547	1,220,745
Payments for Repurchase of Warrants		$ 124,000				$ 50,000		$ 399,500	$ 294,600
warrants outstanding								2,109,098
Accounts Payable, Other						0		$ 0	59,800	0
Liabilities, Fair Value Adjustment						0		0	87,500	0
Call option
Convertible Debt [Abstract]
Purchase of convertible note hedges				$ 117,500
Convertible senior notes
Debt Instrument [Line Items]
Treasury Stock, Value						$ 136,500		$ 136,500	$ 169,500
Interest rate, stated percentage				1.875%		1.875%		1.875%	1.875%
Initial conversion price (in dollars per share)				$ 84.02
Percentage of principal value that holders can require Company to repurchase				100.00%
Estimated fair value of the liability component				$ 271,100
Carrying amount of equity component				120,900
Gross proceeds from the issuance of the Notes				$ 392,000
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						$ 11,154		$ 11,154	$ 169,400
Unamortized discount						(352)		(352)	(22,627)
Convertible Notes Payable						$ 10,802		$ 10,802	146,773
Treasury Stock, Shares						1,625,088		1,625,088
Interest Expense, Debt [Abstract]
Contractual coupon interest rate								$ 544	5,036	7,230
Amortization of discount and note issuance costs								2,818	17,821	22,980
Total interest expense								3,362	22,857	$ 30,210
Convertible Debt [Abstract]
If-converted value in excess of principal								70,400
Credit Facility [Domain]
Line of Credit Facility [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity							$ 750,000
Line of Credit Facility, Expiration Period							5 years
Available increase to the credit facility							$ 250,000
Line of Credit Facility, Current Borrowing Capacity						$ 100,000		100,000
Additional Paid-in Capital
Warrants [Abstract]
Adjustments to Additional Paid in Capital, Other							$ 23,300	(449,456)	(294,552)
Maximum amount of warrant payable								23,317	148,496
Convertible Debt [Abstract]
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments								$ 819,657	$ 691,869
Subsequent Event [Member] | Warrant
Warrants [Abstract]
Reduction of number of warrants					360,406
Payments for Repurchase of Warrants					$ 135,300