Convertible Debt (Details) (USD $)	1 Months Ended		12 Months Ended			3 Months Ended
	Nov. 30, 2014	Oct. 31, 2011	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2015	Jan. 31, 2015
Net carrying amount of the liability component [Abstract]
Total convertible senior notes - par				$ 400,000,000
Convertible Notes Payable, Noncurrent			146,773,000	320,315,000
Treasury Stock, Shares			2,017,732	0
Warrants [Abstract]
Proceeds received from the Warrant		93,800,000
Repayments of Convertible Debt			220,639,000	0	0
Loss on Extinguishment of Debt			33,469,000	0	0
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments			691,869,000
Payments for Repurchase of Warrants			294,552,000	0	0
Maximum number of shares issuable upon exercise of warrants			3,540,095	4,760,840
Maximum reduction of warrants held by warrant holder	493,229
Fair Value Adjustment of Warrants			1,200,000
Maximum amount of warrant payable			(148,496,000)
Maximum share price for warrant holders to close out hedge position	$ 397.75
Convertible Debt [Abstract]
Debt Conversion			230,600,000
Warrant Transactions
Warrants [Abstract]
Strike price of the warrant transaction (in dollars per share)		103.41
Proceeds received from the Warrant		93,800,000
Accounts Payable, Other			59,800,000
Reduction of warrant numbers			202,560
Liabilities, Fair Value Adjustment			87,500,000
Call option
Convertible Debt [Abstract]
Purchase of convertible note hedges		117,500,000
Debt Instrument, Redemption, Criteria One [Member]
Debt Instrument [Line Items]
Number of trading days			20
Number of consecutive trading days			30 days
Percentage of stock price trigger			130.00%
Debt Instrument, Redemption, Criteria Two [Member]
Debt Instrument [Line Items]
Number of trading days			5
Number of consecutive trading days			10 days
Percentage of stock price trigger			98.00%
Debt Instrument, Redemption, Criteria Three [Member]
Debt Instrument [Line Items]
Calendar day period after the record date of equity instruments issuance			60 days
Number of consecutive days			10 days
Convertible senior notes
Debt Instrument [Line Items]
Interest rate, stated percentage		1.875%	1.875%	1.875%
Initial conversion ratio		11.9021
Increment of principal amount for conversion		1,000
Total shares upon conversion (in shares)		4,760,840
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		271,100,000
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%
Net carrying amount of the liability component [Abstract]
Total convertible senior notes - par		400,000,000.0	169,400,000	400,000,000
Unamortized discount			(22,627,000)	(79,685,000)
Convertible Notes Payable, Noncurrent			146,773,000	320,315,000
Interest Expense, Debt [Abstract]
Contractual coupon interest rate			5,036,000	7,230,000	7,503,000
Amortization of discount and note issuance costs			17,821,000	22,980,000	21,623,000
Total interest expense			22,857,000	30,210,000	29,126,000
Warrants [Abstract]
Trading days to calculate settlement			40
Convertible Debt [Abstract]
If-converted value in excess of principal			691,600,000
Additional Paid-in Capital
Warrants [Abstract]
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments			691,869,000
Maximum amount of warrant payable			(148,496,000)
Scenario, Forecast [Member]
Convertible Debt [Abstract]
Debt Conversion						6,700,000
Subsequent Event [Member] | Warrant Transactions
Warrants [Abstract]
Accounts Payable, Other							$ 62,000,000
Reduction of warrant numbers						206,480