Leases - Operating lease costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Leases
Operating lease costs	$ 2,215
Research and Development Expense
Leases
Operating lease costs	1,638
Selling and Marketing Expense
Leases
Operating lease costs	262
General and Administrative Expense
Leases
Operating lease costs	$ 315