Convertible Senior Notes - Interest expense (Details) $ in Thousands	6 Months Ended
Jun. 30, 2020 USD ($)
Debt Instrument [Line Items]
Amortization of Financing Costs and Discounts, Total	$ 557
2.75% Convertible Senior Notes due 2027
Debt Instrument [Line Items]
Contractual interest expense	417
Amortization of debt discount	523
Amortization of debt issuance costs	34
Amortization of Financing Costs and Discounts, Total	$ 974
Interest rate at period end	9.50%
Unamortized debt discount	$ 97,200
Unamortized debt discount amortization period	6 years 10 months 24 days
Debt issuance costs	$ 6,300

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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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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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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