C. Investments

As of December 31, 2012 and 2011, our investments equaled $180.8 million and $166.2 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 December 31, 2012 and 2011 (in thousands):

	December 31, 2012

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair 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

	December 31, 2011

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term investments:
Corporate debt securities
Due in one year or less	$	74,687	$	81	$	(115	)	$	74,653
Due in one to three years		19,950		73		(50	)		19,973
U.S. treasury and government agency securities
Due in one year or less		26,770		67		(7	)		26,830
Due in one to three years		21,028		228		—			21,256
Commercial paper
Due in one year or less		5,997		—		(6	)		5,991

Total short-term investments	$	148,432	$	449	$	(178	)	$	148,703

Long-term investments:
Auction rate securities
Due after five years		19,900		—		(2,373	)		17,527

Total long-term investments	$	19,900	$	—	$	(2,373	)	$	17,527

Total investments	$	168,332	$	449	$	(2,551	)	$	166,230

Auction Rate Securities

In June 2012, we sold our remaining ARS portfolio, with a par value of $19.8 million, for proceeds of $18.3 million and recognized a loss of approximately $1.5 million in other income (expense) in our consolidated statement of operations for the year ended December 31, 2012.

Impairments and Unrealized Gains and Losses on Investments

The following is a summary of the fair value of our investments with unrealized losses that are deemed to be temporarily impaired and their respective gross unrealized losses aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position as of December 31, 2012 and 2011 (in thousands):

	December 31, 2012

	Less than 12 Months					12 Months or Greater				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Corporate debt securities	$	37,036	$	(43	)	$	—	$	—	$	37,036	$	(43	)
U.S. treasury and government agency securities		6,271		(2	)		—		—		6,271		(2	)
Commercial paper		3,992		(4	)		—		—		3,992		(4	)

	$	47,299	$	(49	)	$	—	$	—	$	47,299	$	(49	)

	December 31, 2011

	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Corporate debt securities	$	34,097	$	(161	)	$	4,124	$	(4	)	$	38,221	$	(165	)
U.S. treasury and government agency securities		8,841		(7	)		—		—			8,841		(7	)
Commercial paper		5,991		(6	)		—		—			5,991		(6	)
Auction rate securities		—		—			19,900		(2,373	)		19,900		(2,373	)

	$	48,929	$	(174	)	$	24,024	$	(2,377	)	$	72,953	$	(2,551	)

We did not recognize any unrealized other-than-temporary impairment losses in our consolidated statements of operations related to our securities during either of the years ended December 31, 2012 or 2011. 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. During 2012, we recorded realized losses of $1.5 million to our consolidated statement of operations related to the sale of our then remaining ARS portfolio, as discussed above.