Convertible Notes - Debt issuance costs and interest expense (Details) - Convertible Notes $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Interest expense related to the Convertible Notes
Contractual interest expense	$ 503	$ 1,006
Amortization of debt issuance costs	211	419
Amortization of debt discount	2,042	4,048
Total	$ 2,756	$ 5,473
Effective interest rate of the liability component	7.10%	7.10%
Amortization and interest expense capitalized	$ 743	$ 1,208

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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