Convertible Senior Notes - Summary of Total Interest Expense Recognized Related To Convertible Senior Notes (Details) - Convertible Senior Notes - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Amortization of debt discount and transaction costs	$ 4,616	$ 499
Total interest expense	6,341	691
1.50% Coupon
Debt Instrument [Line Items]
Interest expense	$ 1,725	$ 192

Amount of amortization expense attributable to debt discount (premium) and debt issuance costs.

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

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