Fair Value Measurements (Tables)

9 Months Ended

Sep. 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 September 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	$	11,441,399	$	11,441,399	$	—	$	—
U.S. Treasury securities		25,008,649		—		25,008,649		—
Total cash equivalents	$	36,450,048	$	11,441,399	$	25,008,649	$	—
Short-term investments:
Asset-backed securities	$	19,482,434	$	—	$	19,482,434	$	—
Commercial paper		98,181,285		—		98,181,285		—
Corporate debt securities		54,423,475		—		54,423,475		—
U.S. Treasury securities		29,418,434		—		29,418,434		—
Total short-term investments	$	201,505,628	$	—	$	201,505,628	$	—
Total financial assets	$	237,955,676	$	11,441,399	$	226,514,277	$	—
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 nine months ended September 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 September 30, 2017	$	—