Debt - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Convertible Debt
Debt Instrument [Line Items]
Contractual interest expense	$ 1,445	$ 1,445	$ 2,891	$ 2,891
Amortization of debt discount	1,955	1,955	3,911	3,911
Amortization of debt issuance costs	115	115	229	229
Total interest expense	3,515	3,515	7,031	7,031
Term Loan | Secured Debt
Debt Instrument [Line Items]
Contractual interest expense	1,210	1,173	2,390	2,267
Amortization of debt discount	333	333	666	666
Amortization of debt issuance costs	40	40	80	80
Total interest expense	$ 1,583	$ 1,546	$ 3,136	$ 3,013