Income Tax Disclosure Reconciliation of Federal Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure - Reconciliation of Federal Tax Rate [Abstract]
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	$ (16,035)	$ (14,491)	$ (13,464)
Income Tax Reconciliation, State and Local Income Taxes	0	17	46
Income Tax Reconciliation, Nondeductible Expense	482	468	414
Effective income tax reconciliation, Statutory to GAAP adjustments	109	(640)	(221)
Income Tax Reconciliation, Nondeductible Expense, Share-based Compensation Cost	(3,268)	(570)	(394)
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount	460	(368)	(153)
Income Tax Reconciliation, Tax Credits	(2,391)	(990)	(1,656)
Income Tax Reconciliation, Other Adjustments	(2,385)	788	(1,824)
Effective Income Tax Rate Reconciliation, Change related to Prior Years	(553)	4,006	(4,800)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	0	0	1,835
Income Tax Reconciliation, Change in Deferred Tax Assets Valuation Allowance	24,257	12,404	20,417
Income Tax Expense (Benefit)	$ 676	$ 624	$ 200