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

9 Months Ended

Sep. 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 September 30, 2013 and December 31, 2012 (in thousands):

September 30, 2013

	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
Cash	$	31,706	$	—	$	—		$	31,706
Cash equivalents:
Money market mutual funds	142,968		—		—			142,968
Total cash and cash equivalents	174,674		—		—			174,674
Short-term investments:
Corporate bonds	39,518		57		(20		)	39,555
U.S. agency securities	32,235		45		(6		)	32,274
Asset-backed securities	13,968		9		(20		)	13,957
U.S. Treasury securities	17,760		58		—			17,818
Total short-term investments	103,481		169		(46		)	103,604
Cash, cash equivalents and short-term investments	$	278,155	$	169	$	(46	)	$	278,278

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 September 30, 2013:

	Amortized Cost		Estimated Fair Value
Less than 1 year	$	8,828	$	8,834
Due in 1 to 5 years	94,653		94,770
Total	$	103,481	$	103,604