Long-Term Debt (Schedule of Long-term Debt Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Long-term debt, gross	$ 690,000	$ 460,000
Less: Unamortized debt discounts and fees	164,661	88,750
Long-term Debt, Total	525,339	371,250
Long-term debt outstanding	525,339	371,250
Convertible Senior Notes 3.25% [Member]
Long-term debt, gross	460,000	$ 460,000
Convertible Senior Notes 2.00% Due 2026 [Member]
Long-term debt, gross	$ 230,000

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt discount.

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