4. Fair Value of Financial Instruments Including Cash, Cash Equivalents and Investments

The following tables present, for each of the fair value levels, the Company’s assets that are measured at fair value on a recurring basis at September 30, 2019 and at December 31, 2018:

	At September 30, 2019
	Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs)		Significant Other Observable Inputs (Level 2 Inputs)		Significant Unobservable Inputs (Level 3 Inputs)		Total
Cash equivalents:
Money market funds	$	5,056	$	—	$	—	$	5,056
Investments:
Certificates of deposit		—		134,808		—		134,808
Total	$	5,056	$	134,808	$	—	$	139,864

	At December 31, 2018
	Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs)		Significant Other Observable Inputs (Level 2 Inputs)		Significant Unobservable Inputs (Level 3 Inputs)		Total
Cash equivalents:
Money market funds	$	24	$	—	$	—	$	24
Investments:
Certificates of deposit		—		122,800		—		122,800
Total	$	24	$	122,800	$	—	$	122,824

Certificates of deposit at September 30, 2019 and December 31, 2018 had maturity dates of one year or less.

The Company measures eligible assets and liabilities at fair value with changes in value recognized in earnings. There were no liabilities that were measured at fair value as of September 30, 2019 and December 31, 2018. Fair value treatment may be elected either upon initial recognition of an eligible asset or liability or, for an existing asset or liability, if an event triggers a new basis of accounting. The Company did not elect to remeasure any of its existing financial assets and did not elect the fair value option for any financial assets transacted during the nine months ended September 30, 2019 or the year ended December 31, 2018.

The Company considers all highly liquid investments with an original maturity of 90 days or less at the date of purchase to be cash equivalents. Investments not classified as cash equivalents with maturities one year or less from the balance sheet date are classified as short-term investments, while investments with maturities in excess of one year from the balance sheet date are classified as long-term investments. Management determines the appropriate classification of investments at the time of purchase and re-evaluates such determination at each balance sheet date.

Cash and cash equivalents primarily consist of cash on deposit with banks, and amounts held in interest-bearing money market accounts. Cash equivalents are carried at cost, which approximates their fair market value.

The following is a summary of cash, cash equivalents, and investments as of September 30, 2019 and December 31, 2018:

	At September 30, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Cash and cash equivalents due in 90 days or less	$	29,514	$	—	$	—	$	29,514
Investments:
Certificates of deposit due in one year or less		134,808		—		—		134,808
Total cash, cash equivalents, and investments	$	164,322	$	—	$	—	$	164,322

	At December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Cash and cash equivalents due in 90 days or less	$	34,887	$	—	$	—	$	34,887
Investments:
Certificates of deposit due in one year or less		122,800		—		—		122,800
Total cash, cash equivalents, and investments	$	157,687	$	—	$	—	$	157,687