Investments - Summary of Investments Included in Cash Equivalents and Short Term Investments (Details) - USD ($)	Jun. 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	$ 254,993,384	$ 122,338,668
Cash equivalents and short-term investments, Unrealized Gains	2,147
Cash equivalents and short-term investments, Unrealized Losses	(50,793)	(73,308)
Cash equivalents and short-term investments, Fair Value	254,944,738	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	35,781,822	44,181,756
Cash equivalents and short-term investments, Fair Value	35,781,822	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	20,160,567	7,428,021
Cash equivalents and short-term investments, Unrealized Gains	1,279
Cash equivalents and short-term investments, Unrealized Losses	(2,074)	(6,318)
Cash equivalents and short-term investments, Fair Value	20,159,772	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	85,895,613	34,882,298
Cash equivalents and short-term investments, Fair Value	85,895,613	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	64,147,033	26,905,815
Cash equivalents and short-term investments, Unrealized Gains	813
Cash equivalents and short-term investments, Unrealized Losses	(35,971)	(49,532)
Cash equivalents and short-term investments, Fair Value	64,111,875	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	49,008,349	8,940,778
Cash equivalents and short-term investments, Unrealized Gains	55
Cash equivalents and short-term investments, Unrealized Losses	(12,748)	(17,458)
Cash equivalents and short-term investments, Fair Value	$ 48,995,656	$ 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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