Stockholders' Equity - Stock-Based Compensation Expense (Details) - USD ($)	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Stock-based compensation expense
Total stock-based compensation expense	$ 1,614,185	$ 1,822,148
Research and Development
Stock-based compensation expense
Total stock-based compensation expense	688,972	736,030
General and Administrative Expense.
Stock-based compensation expense
Total stock-based compensation expense	$ 925,213	$ 1,086,118

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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