INVESTMENTS

We classified all of our investments as “available-for-sale” as of December 31, 2015 and 2014. Accordingly, we state our investments at estimated fair value. Fair values are determined based on quoted market prices or pricing models using current market rates. We deem all investments to be available to meet current working capital requirements.

The following is a summary of our investments:



	December 31, 2015								December 31, 2014
Cash equivalents and available- for-sale investments, In thousands	Amortized Cost		Accumulated Other Comprehensive Income				Estimated Fair Value		Amortized Cost		Accumulated Other Comprehensive Income				Estimated Fair Value
	Amortized Cost		Gains		Losses		Estimated Fair Value		Amortized Cost		Gains		Losses		Estimated Fair Value
Commercial paper	$	9,996	$	—	$	—	$	9,996	$	9,998	$	—	$	—	$	9,998
Money market funds	9,074		—		—		9,074		26,456		—		—		26,456
U.S. treasury bills and notes	56,929		1		58		56,872		3,918		1		—		3,919
Securities and obligations of U.S. government agencies	128,343		3		323		128,023		187,947		4		126		187,825
Total	$	204,342	$	4	$	381	$	203,965	$	228,319	$	5	$	126	$	228,198

The following is a reconciliation of our investments to the balance sheet classifications at December 31, 2015 and 2014:



In thousands	2015		2014
Cash equivalents	$	15,072	$	26,456
Short-term investments	188,893		201,742
Investments, at estimated fair value	$	203,965	$	228,198

Gross realized gains and losses on sales of investments were insignificant in each of the years ended December 31, 2015, 2014 and 2013.

The gross amortized cost and estimated fair value of our investments at December 31, 2015, by contractual maturity, are shown below. Expected maturities will differ from contractual maturities because the issuers of the securities may have the right to prepay obligations without prepayment penalties.



In thousands	Gross Amortized Cost		Fair Value
Due in one year or less	$	155,342	$	155,177
Due after one year through five years	49,000		48,788
Total	$	204,342	$	203,965

The following table provides the breakdown of the cash equivalents and investments with unrealized losses at December 31, 2015:



	In Loss Position for Less Than 12 Months				In Loss Position for More Than 12 Months				Total
Investments, In thousands	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
U.S. treasury bills and notes	$	51,872	$	58	$	—	$	—	$	51,872	$	58
Securities and obligations of U.S. government agencies	110,345		323		—		—		110,345		323
Total	$	162,217	$	381	$	—	$	—	$	162,217	$	381

The following table provides the breakdown of the cash equivalents and investments with unrealized losses at December 31, 2014:



	In Loss Position for Less Than 12 Months				In Loss Position for More Than 12 Months				Total
Investments, In thousands	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Securities and obligations of U.S. government agencies	$	152,784	$	126	$	—	$	—	$	152,784	$	126
Total	$	152,784	$	126	$	—	$	—	$	152,784	$	126

We review our investment portfolio regularly for impairment. A security is considered impaired when its fair value is less than its cost basis. If we intend to sell an impaired debt security or it is more likely than not that we will be required to sell it prior to recovery of its amortized cost basis, and other-than-temporary-impairment (“OTTI”) is deemed to have occurred. In these instances, the OTTI loss is recognized in earnings equal to the entire difference between the debt security’s amortized cost basis and its fair value at the balance sheet date.

If we do not intend to sell an impaired debt security and it is not more likely than not that we will be required to sell it prior to recovery of its amortized cost basis, we must determine whether it will recover its amortized cost basis. If we conclude it will not, a credit loss exists and the resulting OTTI is separated into:


•	The amount representing the credit loss, which is recognized in earnings, and


•	The amount related to all other factors, which is recognized in other comprehensive income.

As part of this assessment we will consider the various characteristics of each security, including, but not limited to the following: the length of time and the extent to which the fair value has been less than the amortized cost basis; adverse conditions specifically related to the security, an industry, or a geographic area; the payment structure of the debt security; failure of the issuer of the security to make scheduled interest or principal payments; any changes to the rating of the security by a rating agency and related outlook or status; recoveries or additional declines in fair value subsequent to the balance sheet date. The relative importance of this information varies based on the facts and circumstances surrounding each security, as well as the economic environment at the time of assessment.

We have not recorded any OTTI on our investments for the years ended December 31, 2015, 2014 and 2013.