Income Taxes (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Unrecognized tax benefits	$ 0	$ 0
Accrual for interest or penalties	0	0
Recognized interest and penalties	0	$ 0
Domestic Tax Authority [Member]
Income Tax Disclosure [Line Items]
Reduction of operating losses and credits	341,300,000
Income tax net operating loss carryforwards	305,600,000
Domestic Tax Authority [Member] | Research Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Reduction of operating losses and credits	15,500,000
California research and development tax credit carryforwards	10,800,000
Domestic Tax Authority [Member] | Expiring 2034 [Member]
Income Tax Disclosure [Line Items]
Income tax net operating loss carryforwards	183,800,000
Domestic Tax Authority [Member] | Carryforward Indefinitely [Member]
Income Tax Disclosure [Line Items]
Income tax net operating loss carryforwards	121,800,000
State and Local Jurisdiction [Member]
Income Tax Disclosure [Line Items]
Reduction of operating losses and credits	170,900,000
Income tax net operating loss carryforwards	227,200,000
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
California research and development tax credit carryforwards	$ 16,700,000