Convertible Notes - Interest Expense Incurred (Details) - Convertible Debt - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Debt Instrument [Line Items]
Accrued coupon interest expense	$ 1,471	$ 1,471
Amortization of debt discounts	1,365	1,200
Amortization of deferred financing offering costs	177	157
Total convertible notes interest expense	3,013	2,828
Related Party
Debt Instrument [Line Items]
Accrued coupon interest expense	137	137
Amortization of debt discounts	127	113
Amortization of deferred financing offering costs	3	3
Total convertible notes interest expense	267	253
Others
Debt Instrument [Line Items]
Accrued coupon interest expense	1,334	1,334
Amortization of debt discounts	1,238	1,087
Amortization of deferred financing offering costs	174	154
Total convertible notes interest expense	$ 2,746	$ 2,575