Provision for Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Valuation allowance increased value	$ 12,200,000	$ 10,200,000	$ 7,600,000
Net operating loss carryforwards	70,900,000
Interest or penalties accrued	0	0	0
Liability related to uncertain tax positions	0
Reserve for unrecognized tax benefits	1,084,000	$ 622,000	$ 242,000	$ 19,000
Federal
Income Taxes [Line Items]
Net operating loss carryforwards	$ 47,400,000
Net operating loss carryforwards, expiration year	2035
Net operating loss carryforwards amount with no expiration date	$ 23,600,000
Federal | Earliest Tax Year | U.S.
Income Taxes [Line Items]
Open tax year	2015
Federal | Latest Tax Year | U.S.
Income Taxes [Line Items]
Open tax year	2018
Federal | Research
Income Taxes [Line Items]
Research tax credits	$ 3,600,000
Research tax credits, expiration year	2035
State
Income Taxes [Line Items]
Net operating loss carryforwards	$ 15,400,000
Net operating loss carryforwards, expiration year	2035
State | Earliest Tax Year | California
Income Taxes [Line Items]
Open tax year	2015
State | Latest Tax Year | California
Income Taxes [Line Items]
Open tax year	2018
State | Research
Income Taxes [Line Items]
Research tax credits	$ 3,100,000
Foreign Tax Authority | Earliest Tax Year | Australian Taxation Office
Income Taxes [Line Items]
Open tax year	2017
Foreign Tax Authority | Latest Tax Year | Australian Taxation Office
Income Taxes [Line Items]
Open tax year	2018