Stockholders' Equity - Stock-Based Compensation Expense (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Stock-based compensation expense
Total stock-based compensation expense	$ 1,822,148	$ 1,382,443
Research and Development
Stock-based compensation expense
Total stock-based compensation expense	736,030	507,822
General and Administrative Expense.
Stock-based compensation expense
Total stock-based compensation expense	$ 1,086,118	$ 874,621