Borrowings - Interest Expense (Details) - Convertible Senior Notes - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Interest expense - stated coupon rate	$ 3,695	$ 5,175	$ 14,045	$ 15,525
Amortization of debt discount	2,388	3,128	8,852	9,241
Total interest expense - convertible notes	$ 6,083	$ 8,303	$ 22,897	$ 24,766

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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