Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2013

Fair Value of Financial Instruments [Abstract]

Financial assets measured and recognized at fair value on a recurring basis and classified under appropriate level of fair value hierarchy

As of March 31, 2013, financial assets measured and recognized at fair value on a recurring basis and classified under the appropriate level of the fair value hierarchy as described above was as follows (in thousands):

March 31, 2013	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	12,333		—		—	$	12,333
Commercial paper		—		3,199		—		3,199
Short-term marketable investments:
U.S. government notes		—		4,006		—		4,006
U.S. government agencies		—		32,292		—		32,292
Municipal securities		—		5,482		—		5,482
Commercial paper		—		10,964		—		10,964
Corporate debt securities		—		18,077		—		18,077
Total assets at fair value	$	12,333	$	74,020	$	—	$	86,353

As of December 31, 2012, financial assets measured and recognized at fair value on a recurring basis and classified under the appropriate level of the fair value hierarchy as described above was as follows (in thousands):

December 31, 2012	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	17,348		—		—	$	17,348
Commercial paper		—		4,000		—		4,000
Short-term marketable investments:
U.S. government notes		—		4,009		—		4,009
U.S. government agencies		—		24,958		—		24,958
Municipal securities		—		4,206		—		4,206
Commercial paper		—		10,519		—		10,519
Corporate debt securities		—		18,334		—		18,334
Total assets at fair value	$	17,348	$	66,026	$	—	$	83,374