Income Taxes - Deferred income tax assets and liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforward	$ 34,529	$ 18,636
Tax credits	7,459	4,121
Intangibles	1,914	1,554
Other	1,379	366
Total deferred tax assets	45,281	24,677
Fixed assets	233	133
Total deferred tax liabilities	233	133
Valuation allowance	(45,048)	(24,544)
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued [Abstract]
Unrecognized benefit - beginning of period	1,396	915
Current period tax position increases	1,097	457
Prior period tax position increases	90	24
Unrecognized benefit - end of period	$ 2,583	$ 1,396