Short-term Investments

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Short-term Investments

Short-term Investments

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

Type of securities as of December 31, 2018	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Corporate debt securities	$	47,299	$	1	$	(21	)	$	47,279
U.S. government-related debt securities	14,972		—		(11		)	14,961
Asset-backed securities	$	7,410	$	—	$	(9	)	$	7,401
Total available-for-sale securities	$	69,681	$	1	$	(41	)	$	69,641

Type of securities as of December 31, 2017	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Corporate debt securities	$	35,567	$	—	$	(53	)	$	35,514
U.S. government-related debt securities	15,951		—		(46		)	15,905
Total available-for-sale securities	$	51,518	$	—	$	(99	)	$	51,419

The fair values of available-for-sale securities by contractual maturity at December 31 were as follows (in thousands):

	2018		2017
Maturing in one year or less	$	69,641	$	39,985
Maturing in one to three years	—		11,434
Total available-for-sale securities	$	69,641	$	51,419

The Company has the 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 December 31, 2018 (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	$	14,957	$	(15	)	$	2,516	$	(6	)	$	17,473	$	(21	)
U.S. government-related debt securities	14,961		(11		)	—		—			14,961		(11		)
Asset-backed securities	7,401		(9		)	—		—			7,401		(9		)
Total	$	37,319	$	(35	)	$	2,516	$	(6	)	$	39,835	$	(41	)

The Company invests in securities that are rated investment grade or better. The unrealized losses on investments as of December 31, 2018 and December 31, 2017 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 December 31, 2018, there were no investments in its portfolio that were other-than-temporarily impaired.