Convertible Notes Convertible Notes (Interest Expense for December 2021 Notes) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Debt Instrument [Line Items]
Debt Instrument, Convertible, Beneficial Conversion Feature	$ 1,794	$ 1,626	$ 3,560	$ 3,225
December 2021 Notes [Member]
Debt Instrument [Line Items]
Contractual coupon interest	1,032	1,031	2,063	2,062
Amortization of debt issuance costs	20	19	40	38
Amortization of debt discount	138	135	276	269
Interest Expense, Debt	$ 2,984	$ 2,811	$ 5,939	$ 5,594

Amortization of debt issuance costs

No definition available.

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- Definition

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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- Definition

Amount of a favorable spread to a debt holder between the amount of debt being converted and the value of the securities received upon conversion. This is an embedded conversion feature of convertible debt issued that is in-the-money at the commitment date.

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- Definition

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.

+ References

No definition available.

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- Definition

Amount of the cost of borrowed funds accounted for as interest expense for debt.

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- Definition

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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