3. Marketable Securities and Fair Value Measurements

As of December 31, 2015, marketable securities by security type consisted of:

 

		Amortized Cost				Gross Unrealized Gains				Gross Unrealized Losses				Estimated Fair Value
Certificates of Deposit (due within one year)		$	13,709			$	—			$	—			$	13,709
Certificates of Deposit (due after one year through two years)			1,178				—				—				1,178
United States Treasury Notes (due within one year)			22,596				—				(47	)			22,549
United States Treasury Notes (due after one year through two years)			2,506				—				(8	)			2,498
Total		$	39,989			$	—			$	(55	)		$	39,934

The Company did not have marketable securities as of December 31, 2014.

The following tables present the Company’s fair value hierarchy for its cash equivalents and marketable securities, which are measured at fair value on a recurring basis as of December 31, 2015 and 2014:

 

		Fair Value Measurements at December 31, 2015 Using
		Level 1				Level 2				Level 3				Total
Cash equivalents:
Money Market Instruments		$	—			$	18,361			$	—			$	18,361
Marketable securities:
Certificates of Deposit			—				14,887				—				14,887
United States Treasury Notes			—				25,047				—				25,047
Total		$	—			$	58,295			$	—			$	58,295

 

		Fair Value Measurements at December 31, 2014 Using
		Level 1				Level 2				Level 3				Total
Cash equivalents:
Money Market Instruments		$	—			$	91,316			$	—			$	91,316
Total		$	—			$	91,316			$	—			$	91,316

The carrying values of accounts payable and accrued expenses approximate their fair value due to the short-term nature of these liabilities.