2. Changes to fair value measurement Level 3 (Details) - Liability [Member] - Fair Value, Inputs, Level 3 [Member] - Fair Value, Measurements, Recurring [Member] - Embedded Derivative Liability [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value beginning balance	$ 0
Issuance of Series A redeemable convertible preferred stock with embedded derivative	21,232
Remeasurement of Series A redeemable convertible preferred stock embedded derivative to fair value	(3,258)
Fair value ending balance	$ 17,974