Estimated Fair Value of Financial Instruments - Debt Instruments (Details) - Senior Notes - Level 2 - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Convertible debt, fair value	$ 7,106	$ 7,055
Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Convertible debt, fair value	$ 28,900	$ 20,100

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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