Investment in Equity Securities, at fair value and long-term investments - Summary of Long-term investment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Long Term Investments [Line Items]
Total	$ 27,569	$ 14,038
Black Belt TX Limited [Member] | Equity Securities [Member]
Schedule Of Long Term Investments [Line Items]
Available-for-sale debt securities - Convertible loan	83
Equity securities without readily determinable fair value:	2,250	2,250
Juventas Cell Therapy Ltd [Member] | Equity Securities [Member]
Schedule Of Long Term Investments [Line Items]
Equity securities without readily determinable fair value:	25,035	11,355
Juventas Cell Therapy Ltd [Member] | Put option
Schedule Of Long Term Investments [Line Items]
Equity securities without readily determinable fair value:	$ 201	$ 433