Long-Term Debt (Schedule of Long-term Debt Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Long-term debt, gross	$ 690,000	$ 690,000
Less: Unamortized debt discounts and fees	(151,032)	(157,922)
Long-term Debt, Total	538,968	532,078
Long-term debt outstanding	538,968	532,078
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	$ 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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