Cash, cash equivalents and short-term investments

Cash equivalents consist of highly liquid fixed-income investments with original maturities of three months or less at the time of purchase, including money market funds. Short-term investments consist of readily marketable securities with a remaining maturity of more than three months from time of purchase. The Company classifies all of its cash equivalents and short-term investments as “available for sale,” as these investments are free of trading restrictions. These marketable securities are carried at fair value, with the unrealized gains and losses, net of tax, reported as accumulated other comprehensive income and included as a separate component of stockholders’ equity. Gains and losses are recognized when realized. When the Company determines that an other-than-temporary decline in fair value has occurred, the amount of the decline that is related to a credit loss is recognized in earnings. Gains and losses are determined using the specific identification method. The Company’s realized gains and losses in the three and nine months ended September 30, 2013 and 2012 were insignificant.

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

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

As of September 30, 2013, the Company did not consider any of its investments to be other-than-temporarily impaired.