Income Taxes - Components of deferred tax assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Research and development tax credit carryforwards	$ 1,674	$ 238
Share-based compensation	6,271	3,746
Operating lease liability	1,764	712
Accrued bonus	1,208	855
Accrued expenses and other liabilities	634	223
Net operating losses	198	190
Total deferred tax assets	11,749	5,964
Valuation allowance	(9,307)	(330)	$ (49)	$ (27)
Deferred tax liabilities:
Depreciation and amortization	(786)	(745)
Right of use Asset	(1,646)	(517)
Net deferred tax assets	10	4,372
Foreign
Deferred tax assets:
Research and development tax credit carryforwards	1,383	228
State
Deferred tax assets:
Research and development tax credit carryforwards	$ 844	$ 265