Short-term Investments

3 Months Ended

Mar. 31, 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 March 31, 2014	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
U.S. government-related debt securities	$	1,550	$	1	$	—		$	1,551
Corporate debt securities		55,278		26		(18	)		55,286
Total available-for-sale securities	$	56,828	$	27	$	(18	)	$	56,837

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	March 31, 2014		December 31, 2013
Maturing in one year or less	$	53,286	$	26,725
Maturing after one year through three years		3,551		5,990
Total available-for-sale securities	$	56,837	$	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 approximately $1,900 and $0 for the three months ended March 31, 2014 and 2013, respectively. There were no realized losses on sales of available-for-sale securities for the three months ended March 31, 2014 and 2013.