Borrowings - Interest Expense (Details) - Convertible Senior Notes - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Debt Instrument [Line Items]
Interest expense - stated coupon rate	$ 5,175	$ 5,175	$ 10,350	$ 10,350
Amortization of debt discount	3,247	3,071	6,464	6,113
Total interest expense - convertible notes	$ 8,422	$ 8,246	$ 16,814	$ 16,463

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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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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