3. Cash Equivalents and Marketable Securities

The following tables summarize the estimated fair value of the Company’s cash equivalents and marketable securities and the gross unrealized gains and losses (in thousands):

	September 30, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash equivalents:
Money market funds	$	3,959	$	—	$	—		$	3,959
Reverse repurchase agreements		7,250		—		—			7,250
Total cash equivalents		11,209		—		—			11,209

Marketable securities:
U.S. treasury securities		2,509				(2	)		2,507
U.S. government securities		40,110		—		(30	)		40,080
Total marketable securities	$	42,619	$	—	$	(32	)	$	42,587

	December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash equivalents:
Money market funds	$	4,584	$	—	$	—		$	4,584
Reverse repurchase agreements		39,250		—		—			39,250
Total cash equivalents		43,834		—		—			43,834

Marketable securities:
U.S. government securities		15,758		—		(4	)		15,754
Total marketable securities	$	15,758	$	—	$	(4	)	$	15,754

The reverse repurchase agreements are settled in cash nightly, and as such are classified as cash equivalents.

As of September 30, 2017 and December 31, 2016, the Company held 24 and nine debt securities, respectively, that were in an unrealized loss position for less than one year. The aggregate fair value of debt securities in an unrealized loss position as of September 30, 2017 and December 31, 2016 were $36.8 million and $15.8 million, respectively, with no individual securities in a significant unrealized loss position. The Company evaluated its securities for other-than-temporary impairment and considered the decline in market value for the securities to be primarily attributable to current economic and market conditions and would not be required to sell the securities before recovery of the amortized cost basis. Based on this analysis, these marketable securities were not considered to be other-than-temporarily impaired as of September 30, 2017 and December 31, 2016.

The following tables summarizes the contractual maturities of the Company’s marketable securities at estimated fair value (in thousands):

	September 30,		December 31,
	2017		2016
Due in one year or less	$	26,619	$	15,754
Due in 1 - 2 years		15,968		—
Total marketable securities	$	42,587	$	15,754

The Company may sell investments at any time for use in current operations even if they have not yet reached maturity. As a result, the Company classifies marketable securities, including securities with maturities beyond twelve months as current assets.