Cash, Cash Equivalents and Short-term Investments (Tables)

6 Months Ended

Jun. 30, 2013

Cash and Cash Equivalents [Abstract]

Summary of Cash and Cash Equivalents and Short-Term Investments

Cash and cash equivalents and short-term investments consisted of the following as of June 30, 2013 and December 31, 2012 (in thousands):

June 30, 2013

	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
Cash	$	45,706	$	—	$	—		$	45,706
Cash equivalents:
Money market mutual funds	31,697		—		—			31,697
Total cash and cash equivalents	77,403		—		—			77,403
Short-term investments:
Corporate bonds	21,471		6		(51		)	21,426
U.S. agency securities	21,126		2		(50		)	21,078
Asset-backed securities	6,669		—		(29		)	6,640
U.S. Treasury securities	5,514		—		(9		)	5,505
Total short-term investments	54,780		8		(139		)	54,649
Cash, cash equivalents and short-term investments	$	132,183	$	8	$	(139	)	$	132,052

December 31, 2012

	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
Cash	$	59,568	$	—	$	—		$	59,568
Cash equivalents:
Money market mutual funds	17,000		—		—			17,000
Total cash and cash equivalents	76,568		—		—			76,568
Short-term investments:
Corporate bonds	13,389		2		(14		)	13,377
U.S. agency securities	11,280		4		(1		)	11,283
Asset-backed securities	4,670		1		(5		)	4,666
U.S. Treasury securities	3,546		2		—			3,548
Total short-term investments	32,885		9		(20		)	32,874
Cash, cash equivalents and short-term investments	$	109,453	$	9	$	(20	)	$	109,442

Cost and Estimated Fair Value of Short-Term Fixed Income Securities

The following table summarizes the cost and estimated fair value of short-term fixed income securities classified as short-term investments based on stated maturities as of June 30, 2013:

	Amortized Cost		Estimated Fair Value
Less than 1 year	$	5,098	$	5,097
Due in 1 to 5 years	49,682		49,552
Total	$	54,780	$	54,649