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Income Taxes - Additional Information (Detail) - USD ($) | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Income Tax Disclosure [Line Items] |  |  |
Provision for income taxes | $ 0 | $ 0 | $ 0
Increase in valuation allowance | 13,400,000 | $ 3,000,000 | $ 2,900,000
Research and development tax credit carryforwards, state | 600,000 |  |
Research and development tax credit carryforwards, federal | $ 1,100,000 |  |
Federal research and development tax credits, expiration start date | 2035 |  |
Earliest Tax Year [Member] |  |  |
Income Tax Disclosure [Line Items] |  |  |
Open tax year | 2012 |  |
Latest Tax Year [Member] |  |  |
Income Tax Disclosure [Line Items] |  |  |
Open tax year | 2016 |  |
Australian Taxation Office [Member] |  |  |
Income Tax Disclosure [Line Items] |  |  |
Accumulated tax losses carry forward | $ 9,200,000 |  |
Domestic Tax Authority [Member] |  |  |
Income Tax Disclosure [Line Items] |  |  |
Accumulated tax losses carry forward | $ 48,000,000 |  |
Net operating loss carryforwards expiration year | 2033 |  |
State and Local Jurisdiction [Member] |  |  |
Income Tax Disclosure [Line Items] |  |  |
Accumulated tax losses carry forward | $ 37,700,000 |  |
Net operating loss carryforwards expiration year | 2033 |  |

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