Convertible Senior Notes (Interest Expense) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Debt Instrument [Line Items]
Amortization of debt issuance costs	$ 562us-gaap_AmortizationOfFinancingCosts	$ 320us-gaap_AmortizationOfFinancingCosts
Amortization of debt discount	4,954	2,595
Senior Notes [Member] \| Convertible Senior Notes Due 2017 [Member]
Debt Instrument [Line Items]
Contractual interest expense	945	945
Amortization of debt issuance costs	360	320
Amortization of debt discount	2,753	2,595
Total interest expense	4,058	3,860
Effective interest rate of the liability component	6.02%	6.02%
Senior Notes [Member] \| Convertible Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Contractual interest expense	2,152	0
Amortization of debt issuance costs	202	0
Amortization of debt discount	2,201	0
Total interest expense	$ 4,555	$ 0
Effective interest rate of the liability component	6.50%	0.00%

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Amount of noncash expense included in interest expense to issue debt and obtain financing associated with the related debt instruments. Alternate captions include noncash interest expense.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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Represents the portion of interest incurred in the period on debt arrangements that was charged against earnings, excluding amortization of debt discount (premium) and financing costs.

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