Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Schedule of Assets Measured at Fair Value on Recurring Basis

Assets measured at fair value on a recurring basis were as follows:

Description	As of June 30, 2018		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents:
Money market mutual funds	$	35,781,822	$	35,781,822	$	—	$	—
Commercial paper		32,876,471		—		32,876,471		—
Corporate debt securities		5,643,984		—		5,643,984		—
U.S. Treasury securities		20,094,911		—		20,094,911		—
Total cash equivalents	$	94,397,188	$	35,781,822	$	58,615,366	$	—
Short-term investments:
Asset-backed securities	$	20,159,772	$	—	$	20,159,772	$	—
Commercial paper		53,019,143		—		53,019,143		—
Corporate debt securities		58,467,890		—		58,467,890		—
U.S. Treasury securities		28,900,745		—		28,900,745		—
Total short-term investments	$	160,547,550	$	—	$	160,547,550	$	—
Total financial assets	$	254,944,738	$	35,781,822	$	219,162,916	$	—
Description	As of December 31, 2017		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents:
Money market mutual funds	$	44,181,756	$	44,181,756	$	—	$	—
Total cash equivalents	$	44,181,756	$	44,181,756	$	—	$	—
Short-term investments:
Asset-backed securities	$	7,421,703	$	—	$	7,421,703	$	—
Commercial paper		34,882,298		—		34,882,298		—
Corporate debt securities		26,856,283		—		26,856,283		—
U.S. Treasury securities		8,923,320		—		8,923,320		—
Total short-term investments	$	78,083,604	$	—	$	78,083,604	$	—
Total financial assets	$	122,265,360	$	44,181,756	$	78,083,604	$	—

Schedule of Reconciliation of Changes in the Fair Value of Financial Instruments

The reconciliation of changes in the fair value of financial instruments based on Level 3 inputs for the six months ended June 30, 2017, consisted of:

Fair value as of January 1, 2017	$	4,247,000
Change in fair value of convertible preferred stock tranche    liability		876,000
Reduction in tranche liability due to preferred stock issuance		(5,123,000	)
Fair value as of June 30, 2017	$	—