Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Deferred income tax expense (benefit)	$ 0	$ 0
Deferred tax assets change in valuation allowance	11,991,000	4,568,000
Deferred tax assets, operating loss carryforwards, domestic	57,279,000	19,007,000
Deferred tax assets, operating loss carryforwards, not subject to expiration	39,774,000
Deferred tax assets, operating loss carryforwards, foreign	1,201,000	$ 296,000
Payroll tax liability capped per year	250,000
Income tax reconciliation tax credit research	$ 250,000
Income tax credit carryforward expiration period	20 years
Percentage of cumulative changes in ownership interest subject to annual limitation	50.00%
Period of cumulative changes in ownership interest	3 years
Research and development payable tax credit, percentage	(1.10%)	(1.30%)
Federal corporate tax rate	21.00%	34.00%
Reduction in deferred tax liabilities	$ (2,779,000)
U.S. federal [Member]
Research and development tax credits carryforwards	339,000	$ 34,000
Australia [Member]
Income tax reconciliation tax credit research	$ 1,300,000
Australia [Member] | Maximum [Member]
Research and development payable tax credit, percentage	43.50%
Expiration Through 2033 [Member] | State [Member]
Research and development tax credits carryforwards	$ 146,000	119,000
Expiration Through 2037 [Member]
Deferred tax assets, operating loss carryforwards, subject to expiration	17,504,000
Expiration Through 2038 [Member]
Deferred tax assets, operating loss carryforwards, state	$ 54,212,000	$ 18,866,000