Short-term Investments

9 Months Ended

Sep. 30, 2014

Investments, Debt and Equity Securities [Abstract]

Short-term Investments

5. Short-term Investments

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

Type of security as of September 30, 2014	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
U.S. government-related debt securities	$	1,518	$	1	$	—		$	1,519
Corporate debt securities		43,877		7		(27	)		43,857
Asset-backed securities		3,300		—		(2	)		3,298
Total available-for-sale securities	$	48,695	$	8	$	(29	)	$	48,674

Type of security as of December 31, 2013	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
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

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

Contractual maturity	September 30, 2014		December 31, 2013
Maturing in one year or less	$	42,872	$	26,725
Maturing in one to three years		5,802		5,990
Total available-for-sale securities	$	48,674	$	32,715

Realized gains and losses are determined based on the specific identification method and are reported in other income in the condensed consolidated statements of operations. Gross realized gains on sales of available-for-sale securities were $3,000 and $5,000 for the three and nine months ended September 30, 2014, respectively. There were no gross realized gains for the three and nine months ended September 30, 2013 and no realized losses on sales of available-for-sale securities for any of the periods presented.