Income Taxes - Narrative (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 115,564,000	$ 114,960,000
Net operating loss carryovers	79,675,000	74,965,000
Unrecognized tax benefits	16,573,000	14,700,000	$ 4,421,000
Unrecognized tax benefits that would impact effective tax rate	13,300,000
Income tax penalties and interest accrued	0	$ 0	$ 0
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	328,000,000
Internal Revenue Service (IRS) | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits carryforward	31,100,000
California
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	276,000,000
California | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits carryforward	9,100,000
After 2017, No Expiration | Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	$ 64,600,000