Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Net deferred tax assets	$ 103,631,000	$ 71,641,000
Net operating loss carryovers	70,739,000	48,912,000
Federal Alternative Minimum Tax Credit carryforwards	$ 200,000
Net operating loss carryforward limitation on use percentage ownership change minimum	50.00%
Unrecognized tax benefits	$ 5,632,000	2,298,000	$ 1,853,000	$ 1,092,000
Unrecognized tax benefits that would not impact effective tax rate	3,700,000
Tax penalties and interest	0	$ 0	$ 0
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	204,800,000
Internal Revenue Service (IRS) | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits carryforward	20,300,000
Internal Revenue Service (IRS) | Stock options
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	19,400,000
California
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	173,200,000
California | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits carryforward	6,900,000
California | Stock options
Operating Loss Carryforwards [Line Items]
Net operating loss carryovers	$ 19,400,000