Short-term Investments

6 Months Ended

Jun. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Short-term investments consisted of available-for-sale securities as follows (in thousands):



Type of securities as of June 30, 2017	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Corporate debt securities	$	47,239	$	—	$	(28	)	$	47,211
U.S. government-related debt securities	11,504		—		(25		)	11,479
Total available-for-sale securities	$	58,743	$	—	$	(53	)	$	58,690



Type of securities as of December 31, 2016	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Corporate debt securities	$	36,198	$	4	$	(42	)	$	36,160
U.S. government-related debt securities	17,312		1		(20		)	17,293
Total available-for-sale securities	$	53,510	$	5	$	(62	)	$	53,453

The fair values of available-for-sale securities by contractual maturity were as follows (in thousands):



	June 30, 2017		December 31, 2016
Maturing in one year or less	$	54,688	$	46,310
Maturing in one to three years	4,002		7,143
Total available-for-sale securities	$	58,690	$	53,453

The Company has both the intent and ability to sell its available-for-sale investments maturing greater than one year within 12 months from the balance sheet date and, accordingly, has classified these securities as current in the consolidated balance sheet.

The following table summarizes investments that have been in a continuous unrealized loss position as of June 30, 2017 (in thousands).



	Less Than 12 Months					12 Months or Greater				Total
	Fair value		Gross unrealized losses			Fair value		Gross unrealized losses		Fair value		Gross unrealized losses
Corporate debt securities	$	31,061	$	(28	)	$	—	$	—	$	31,061	$	(28	)
U.S. government-related debt securities	11,479		(25		)	—		—		11,479		(25		)
Total	$	42,540	$	(53	)	$	—	$	—	$	42,540	$	(53	)

The Company invests in securities that are rated investment grade or better. The unrealized losses on investments as of June 30, 2017 and December 31, 2016 were primarily caused by interest rate increases.

The Company reviews the individual securities in its portfolio to determine whether a decline in a security’s fair value below the amortized cost basis is other-than-temporary. The Company determined that as of June 30, 2017, there were no investments in its portfolio that were other-than-temporarily impaired.