Short-term Investments (Tables)

3 Months Ended

Mar. 31, 2015

Investments, Debt and Equity Securities [Abstract]

Short-Term Investments Available-for-Sale Securities

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

Type of security as of March 31, 2015	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Corporate debt securities	$	38,759	$	1	$	(18	)	$	38,742
Asset-backed securities		2,419		—		(1	)		2,418
Total available-for-sale securities	$	41,178	$	1	$	(19	)	$	41,160

Type of security as of December 31, 2014	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
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

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

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

Contractual maturity	March 31, 2015		December 31, 2014
Maturing in one year or less	$	38,612	$	51,235
Maturing in one to three years		2,548		3,767
Total available-for-sale securities	$	41,160	$	55,002

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 a continuous unrealized loss position for more than 12 months as of March 31, 2015 (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	$	28,340	$	(17	)	$	1,999	$	(1	)	$	30,339	$	(18	)
Asset-backed securities		2,418		(1	)		—		—			2,418		(1	)
Total	$	30,758	$	(18	)	$	1,999	$	(1	)	$	32,757	$	(19	)