Short-term Investments (Tables)

12 Months Ended

Dec. 31, 2014

Investments, Debt and Equity Securities [Abstract]

Short-Term Investments Available-for-Sale Securities

Short-term investments consisted of available-for-sale securities as follows:

Type of security as of December 31, 2014	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
	(In thousands)
U.S. government-related debt securities	$	4,502	$	—	$	(4	)	$	4,498
Corporate debt securities		47,345		2		(40	)		47,307
Asset-backed securities		3,198		—		(1	)		3,197
Total available-for-sale securities	$	55,045	$	2	$	(45	)	$	55,002
Type of security as of December 31, 2013	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
	(In thousands)
U.S. government-related debt securities	$	1,565	$	1	$	—		$	1,566
Corporate debt securities		31,128		24		(3	)		31,149
Total available-for-sale securities	$	32,693	$	25	$	(3	)	$	32,715

Fair Values of Available-for-Sale Securities by Contractual Maturity

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

	2014		2013
	(In thousands)
Maturing in one year or less	$	51,235	$	26,725
Maturing in one to three years		3,767		5,990
Total available-for-sale securities	$	55,002	$	32,715

Summary of Investments in Continuous Unrealized Loss Position for Less Than 12 Months

The following table summarizes investments that have been in a continuous unrealized loss position for less than 12 months and none have been in a continuous unrealized loss position for more than 12 months as of December 31, 2014:

	Less Than 12 Months
	Fair value		Gross unrealized losses
	(In thousands)
U.S. government-related debt securities	$	2,996	$	(4	)
Corporate debt securities		30,372		(40	)
Asset-backed securities		2,259		(1	)
Total	$	35,627	$	(45	)