Income Taxes - Schedule Of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 86,990	$ 73,612
Tax credits	8,329	7,603
Other temporary differences	2,888	3,156
Start-up expenditures	2,716	3,026
Stock option expenses	3,450	3,130
Lease liability	987
Total deferred tax assets	105,360	90,527
Deferred tax asset valuation allowance	(104,204)	(90,361)
Net deferred tax assets	1,156	166
Deferred tax liabilities:
Right of use asset	(859)
Prepaid expenses	$ (297)	$ (166)