Short-term Investments

9 Months Ended

Sep. 30, 2018

Short Term Investments [Abstract]

Short-term Investments

4. Short-term Investments

The Company invests portions of excess cash in United States treasuries with maturities ranging from three to twelve months from the purchase date. These debt securities are classified as short-term investments in the accompanying consolidated balance sheets and are accounted for as available-for-sale securities.

The following table summarizes the Company’s short-term investments accounted for as available-for-sale securities as of September 30, 2018, and December 31, 2017 (in thousands):

	Maturity (in years)	Amortized Cost		Unrealized Losses			Unrealized Gains		Estimated Fair Value
September 30, 2018
U.S. Treasury debt securities	1 or less		27,959		(14	)		—		27,945
Total		$	27,959	$	(14	)	$	—	$	27,945
December 31, 2017
U.S. Treasury debt securities	1 or less		12,000		(3	)		—		11,997
Total		$	12,000	$	(3	)	$	—	$	11,997

The Company reviewed its investment holdings as of September 30, 2018 and determined that the unrealized losses were not other-than-temporary unrealized losses because the Company does not intend to sell the underlying securities prior to maturity and it is not more likely than not that the Company will be required to sell these securities before the recovery of their amortized cost basis. During each of the three and nine months ended September 30, 2018 and 2017, the Company did not recognize any impairment or gains or losses on sales of available-for-sale securities.