Investments - Summary of Investments Included in Cash Equivalents and Short Term Investments (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	$ 237,976,554	$ 122,338,668
Cash equivalents and short-term investments, Unrealized Gains	7,139
Cash equivalents and short-term investments, Unrealized Losses	(28,017)	(73,308)
Cash equivalents and short-term investments, Fair Value	237,955,676	122,265,360
Money Market Mutual Funds
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	11,441,399	44,181,756
Cash equivalents and short-term investments, Fair Value	11,441,399	44,181,756
Asset-backed Securities
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	19,485,610	7,428,021
Cash equivalents and short-term investments, Unrealized Gains	367
Cash equivalents and short-term investments, Unrealized Losses	(3,543)	(6,318)
Cash equivalents and short-term investments, Fair Value	19,482,434	7,421,703
Commercial Paper
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	98,181,285	34,882,298
Cash equivalents and short-term investments, Fair Value	98,181,285	34,882,298
Corporate Debt Securities
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	54,428,208	26,905,815
Cash equivalents and short-term investments, Unrealized Gains	6,772
Cash equivalents and short-term investments, Unrealized Losses	(11,505)	(49,532)
Cash equivalents and short-term investments, Fair Value	54,423,475	26,856,283
U.S Treasury Securities
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	54,440,052	8,940,778
Cash equivalents and short-term investments, Unrealized Losses	(12,969)	(17,458)
Cash equivalents and short-term investments, Fair Value	$ 54,427,083	$ 8,923,320

Schedule of cash, cash equivalents and available-for-sale securities.

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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