Notes Payable Schedule of Interest Expense Recognized Related to Convertible Notes (Details) - Convertible debt - 3.00% Convertible notes $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Contractual interest expense	$ 3,482
Amortization of debt discount	4,641
Amortization of debt issuance	175
Total interest expense	$ 8,298

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-Section S99
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Amount of amortization expense attributable to debt issuance costs.

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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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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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