(2)	Cash, Cash Equivalents and Short-Term Investments

The following table shows the Company’s cash and cash equivalents and short-term investments by significant investment category as of December 31, 2017:

	December 31, 2017
	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value		Cash and Cash Equivalents		Short-Term Investments
Cash	$	3,040,696	$	—		$	3,040,696	$	3,040,696	$	—

Level 1 (1):
Money market funds		8,234,751		—			8,234,751		8,234,751		—
U.S. treasury securities		2,490,799		(5,540	)		2,485,259		—		2,485,259
Subtotal		10,725,550		(5,540	)		10,720,010		8,234,751		2,485,259
Level 2 (2):
Commercial paper		9,716,093		—			9,716,093		—		9,716,093
Corporate debt obligations		6,829,191		(9,414	)		6,819,777		—		6,819,777
Repurchase agreements		3,000,233		—			3,000,233		3,000,233		—
Asset-backed securities		3,018,276		(1,953	)		3,016,323		750,388		2,265,935
Subtotal		22,563,793		(11,367	)		22,552,426		3,750,621		18,801,805

Total	$	36,330,039	$	(16,907	)	$	36,313,132	$	15,026,068	$	21,287,064

(1)	Level 1 fair value estimates are based on quoted prices in active markets for identical assets or liabilities.

(2)

Level 2 fair value estimates are based on observable inputs other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

The Company’s investments were primarily valued based upon one or more valuations reported by its investment accounting and reporting service provider. The investment service provider values the securities using a hierarchical security pricing models that relies primarily on valuations provided by a third-party pricing vendor. Such valuations may be based on trade prices in active markets for identical assets or liabilities (Level 1 inputs) or valuation models using inputs that are observable either directly or indirectly (Level 2 inputs), such as quoted prices for similar assets or liabilities, yield curve, volatility factors, credit spreads, default rates, loss severity, current market and contractual prices for underlying instruments or debt, broker and dealer quotes, as well as other relevant economic measures. The Company performs certain procedures to corroborate the fair value of its holdings, including comparing valuations obtained from its investment service provider with other pricing sources to validate the reasonableness of the valuations.

The Company typically invests in highly-rated securities, and its investment policy limits the amount of credit exposure to any one issuer. The policy requires investments in fixed income instruments denominated and payable in U.S. dollars only and requires investments to be investment grade, with a primary objective of minimizing the potential risk of principal loss.

The following table presents the Company’s short-term investments with unrealized losses by investment category and length of time that individual securities have been in a continuous unrealized loss position as of December 31, 2017:

	Less Than 12 Months
Description of Securities	Estimated Fair Value		Unrealized Losses
December 31, 2017
U.S. treasury securities	$	2,485,259	$	(5,540	)
Corporate debt obligations		6,819,777		(9,414	)
Asset-backed securities		2,265,935		(1,953	)
Total	$	11,570,971	$	(16,907	)

The Company considers the declines in market value of its short-term investments to be temporary in nature. Fair values were determined for each individual security in the investment portfolio. When evaluating an investment for other-than-temporary impairment, the Company reviews factors such as length of time and extent to which fair value has been below its cost basis, the financial condition of the issuer and any changes thereto, changes in market interest rates and the Company’s intent to sell, or whether it is more likely than not it will be required to sell the investment before recovery of the investment’s cost basis. As of December 31, 2017, the Company does not consider any of its investments to be other-than temporarily impaired.

Contractual maturities of short-term investments as of December 31, 2017 are as follows:

	Estimated Fair Value
Due within one year	$	21,287,064
Total	$	21,287,064