Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Research and development credit carryforwards	$ 3,690,000	$ 3,355,000
NOL carryforward reduced amount	800,000
Valuation allowance	43,104,000	51,040,000
Valuation allowance change	7,900,000
Unrecognized tax benefits	0	$ 0
Tax Cuts And Jobs Act Of 2017, reduction in deferred tax asset	14,700,000
Tax Cuts And Jobs Act Of 2017, reduction to deferred tax asset valuation allowance	14,700,000
Accounting Standards Update 2016-09
Income Taxes [Line Items]
Deferred tax assets, net	300,000
Canada Revenue Agency
Income Taxes [Line Items]
Research and development credit carryforwards	4,200,000
Expire beginning 2031 through 2037
Income Taxes [Line Items]
Net operating loss carryforwards, federal	119,300,000
Net operating loss carryforwards, state	118,500,000
Expire beginning 2025 through 2037 | State
Income Taxes [Line Items]
Research and development tax credit carryforward	1,000,000
Expire beginning 2025 through 2037 | Federal
Income Taxes [Line Items]
Research and development tax credit carryforward	2,000,000
Expire beginning 2025 through 2027 | Canada Revenue Agency
Income Taxes [Line Items]
Operating loss carryforwards for Canadian federal taxes	16,800,000
Expire beginning 2032 through 2036 | Investment Tax Credit Carryforward | Canada Revenue Agency
Income Taxes [Line Items]
Canadian federal investment tax credit carryforwards	$ 1,000,000