Short-term Investments

9 Months Ended

Sep. 30, 2018

Investments Debt And Equity Securities [Abstract]

Short-term Investments

3. Short-term Investments

The following table summarizes the held-to-maturity securities held at September 30, 2018 and December 31, 2017 (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
As of December 31, 2017
U.S. government securities	$	11,462	$	74	$	(79	)	$	11,457
Commercial paper		11,962		—		—			11,962
Overnight repurchase agreement		9,000		—		—			9,000
Total short-term investments	$	32,424	$	74	$	(79	)	$	32,419
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
As of September 30, 2018
U.S. government securities	$	14,953	$	11	$	(12	)	$	14,952
Commercial paper		8,955		—		—			8,955
Overnight repurchase agreement		9,500		—		—			9,500
Total short-term investments	$	33,408	$	11	$	(12	)	$	33,407

All held-to-maturity short-term investments at September 30, 2018 and December 31, 2017 will mature in less than one year.  The gross unrealized gains and losses for the Company's commercial paper and overnight repurchase agreement are not significant.  The Company carries short-term investments at amortized cost. The fair value of the short-term investments is determined based on “Level 1” inputs, which consist of quoted prices in active markets for identical assets.