Income Taxes - Narrative (Details)	12 Months Ended			149 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) ownership_change	Dec. 31, 2011 USD ($)	Aug. 31, 2006 USD ($)
Operating Loss Carryforwards [Line Items]
Penalties and interest expense	$ 0	$ 0	$ 0
Penalties and interest accrued	0	0		$ 0
Number of changes in ownership | ownership_change				3
Reduction in deferred tax asset and corresponding decrease in valuation allowance	36,100,000
Less valuation allowance	118,064,000	101,114,000		$ 118,064,000
Income tax expense (benefits)	0	$ 0	$ (948,000)
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses	286,300,000			286,300,000
Tax credit carryforward, amount	3,400,000			3,400,000
Operating loss carryforwards decrease					$ 121,100,000	$ 1,900,000
Tax credit carryforwards, decrease					3,000,000.0	$ 8,000
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, amount	4,100,000			4,100,000
Operating loss carryforwards decrease					$ 53,300,000
State and Local Jurisdiction [Member] | California [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses	190,300,000			190,300,000
Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 191,800,000			$ 191,800,000