Convertible Senior Notes (Interest Expense) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Disclosure [Abstract]
Contractual interest expense	$ 3,781	$ 3,781	$ 2,101
Amortization of debt issuance costs	1,332us-gaap_AmortizationOfFinancingCosts	1,179us-gaap_AmortizationOfFinancingCosts	598us-gaap_AmortizationOfFinancingCosts
Amortization of debt discount	10,588	9,978	5,306
Total interest expense	$ 15,701us-gaap_InterestExpenseDebt	$ 14,938us-gaap_InterestExpenseDebt	$ 8,005us-gaap_InterestExpenseDebt
Effective interest rate of the liability component	6.02%	6.02%

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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