C. Investments

As of September 30, 2013 and December 31, 2012, our investments equaled $182.6 million and $180.8 million, respectively, and consisted of securities classified as available-for-sale in accordance with accounting standards which provide guidance related to accounting and classification of certain investments in debt and equity securities.

The following is a summary of our investments as of September 30, 2013 and December 31, 2012 (in thousands):

	September 30, 2013
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Corporate debt securities
Due in one year or less	$	45,645	$	67	$	(2	)	$	45,710
Due in one to three years	84,020		92		(158		)	83,954
U.S. treasury and government agency securities
Due in one year or less	22,551		25		—			22,576
Due in one to three years	30,321		53		(19		)	30,355
Total investments	$	182,537	$	237	$	(179	)	$	182,595

	December 31, 2012
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Corporate debt securities
Due in one year or less	$	52,332	$	88	$	(6	)	$	52,414
Due in one to three years	59,176		137		(37		)	59,276
U.S. treasury and government agency securities
Due in one year or less	24,795		86		—			24,881
Due in one to three years	34,606		84		(2		)	34,688
Commercial paper
Due in one year or less	9,494		1		(4		)	9,491
Total investments	$	180,403	$	396	$	(49	)	$	180,750

Impairments and Unrealized Losses on Investments

We did not recognize any other-than-temporary impairment losses in our condensed consolidated statements of operations related to our securities during any of the three or nine month periods ended September 30, 2013 and 2012. We considered various factors, including the length of time that each security was in an unrealized loss position and our ability and intent to hold these securities until the recovery of their amortized cost basis occurs. Future events may occur, or additional information may become available, which may cause us to identify credit losses where we do not expect to receive cash flows sufficient to recover the entire amortized cost basis of a security and which may necessitate the recording of future realized losses on securities in our portfolio. Significant losses in the estimated fair values of our investments could have a material adverse effect on our earnings in future periods.

Realized Gains and Losses on Investments

Gains and losses are determined on the specific identification method. Realized gains were insignificant during both the three and nine months ended September 30, 2013. During the nine months ended September 30, 2012 we recorded realized losses of $1.5 million to our condensed consolidated statements of operations related to the sale of our then-remaining auction rate securities portfolio.