Income Taxes - Summary of Company's Pre Tax Earnings (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Before Income Taxes [Line Items]
Total	$ (82,865,874)	$ (31,044,535)
U.K. [Member]
Income Before Income Taxes [Line Items]
Total	(73,359,977)	(26,458,625)
Federal [Member]
Income Before Income Taxes [Line Items]
Total	$ (9,980,287)	$ (4,585,910)