Income Taxes - Additional Information (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
TCJA, NOL and Tax Credit
Federal indefinite net operating loss carry forwards from JOBS act	$ 62,200,000
Valuation allowance	41,253,000	$ 23,459,000	$ 11,724,000
Unrecognized tax benefit	0
U.K.
TCJA, NOL and Tax Credit
Net operating loss carryforwards	91,800,000
U.S. federal
TCJA, NOL and Tax Credit
Net operating loss carryforwards	74,900,000
U.S. federal | Research and development
TCJA, NOL and Tax Credit
Tax credits carryforwards	2,700,000
State
TCJA, NOL and Tax Credit
Net operating loss carryforwards	76,400,000
State | Research and development
TCJA, NOL and Tax Credit
Tax credits carryforwards	$ 1,000,000