Convertible Notes - Interest Expense Incurred (Details) - Convertible Debt - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Debt Instrument [Line Items]
Accrued coupon interest expense	$ 1,471	$ 1,471	$ 2,942	$ 2,943
Amortization of debt discounts	1,409	1,241	2,774	2,442
Amortization of deferred financing offering costs	184	162	361	318
Total convertible notes interest expense	3,064	2,874	6,077	5,703
Related Party
Debt Instrument [Line Items]
Accrued coupon interest expense	137	137	274	275
Amortization of debt discounts	131	117	258	229
Amortization of deferred financing offering costs	4	3	7	6
Total convertible notes interest expense	272	257	539	510
Others
Debt Instrument [Line Items]
Accrued coupon interest expense	1,334	1,334	2,668	2,668
Amortization of debt discounts	1,278	1,124	2,516	2,213
Amortization of deferred financing offering costs	180	159	354	312
Total convertible notes interest expense	$ 2,792	$ 2,617	$ 5,538	$ 5,193