Investments (Tables)

12 Months Ended

Dec. 31, 2015

Investments [Abstract]

Available-for-sale Securities

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
			Gains		Losses						Gains		Losses
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

Fair Value, by Balance Sheet Grouping

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

Investments Classified by Contractual Maturity Date

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

Schedule of Temporary Impairment Losses, Investments

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