Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Income tax examination, likelihood of unfavorable settlement	greater than 50 percent
Uncertain tax positions	$ 1,538,220	$ 0
Accrued interest or penalties	0	0
Recognized interest or penalties	$ 0	$ 0
U.S. federal corporate tax rate	21.00%	34.00%
Tax cuts and jobs act of 2017, change in tax rate, decrease in deferred tax assets	$ 16,232,211
Tax cuts and jobs act of 2017, change in tax rate, net adjustment in deferred tax expense	0
Valuation allowance	38,740,784	$ 35,008,331
Change in valuation reserve	3,732,453
Gross unrecognized tax benefits	1,538,220
Unrecognized tax benefits if recognized would impact effective tax rate	0
Research and Experimental Tax Credits
Income Tax Disclosure [Line Items]
Gross unrecognized tax benefits	1,538,220
Federal
Income Tax Disclosure [Line Items]
NOL carryforwards	138,759,835
State
Income Tax Disclosure [Line Items]
NOL carryforwards	89,208,791
France
Income Tax Disclosure [Line Items]
NOL carryforwards	$ 38,618
Beginning Expiration Year | Federal
Income Tax Disclosure [Line Items]
Tax credit carryforward, expiration year	2021
Beginning Expiration Year | State
Income Tax Disclosure [Line Items]
Tax credit carryforward, expiration year	2019
Maximum
Income Tax Disclosure [Line Items]
U.S. federal corporate tax rate		35.00%
Maximum | Federal
Income Tax Disclosure [Line Items]
NOL carryforward expiration year	2038
Maximum | State
Income Tax Disclosure [Line Items]
NOL carryforward expiration year	2038
Minimum | Federal
Income Tax Disclosure [Line Items]
NOL carryforward expiration year	2021
Minimum | State
Income Tax Disclosure [Line Items]
NOL carryforward expiration year	2027