Investments (Tables)

12 Months Ended

Dec. 31, 2016

Investments [Abstract]

Available-for-sale Securities

The following is a summary of our investments:

	December 31, 2016								December 31, 2015
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	$	23,744	$	—	$	60	$	23,684	$	9,996	$	—	$	—	$	9,996
Money market funds	2,266		—		—		2,266		9,074		—		—		9,074
U.S. treasury bills and notes	29,467		1		7		29,461		56,929		1		58		56,872
Securities and obligations of U.S. government agencies	127,961		8		265		127,704		128,343		3		323		128,023
Total	$	183,438	$	9	$	332	$	183,115	$	204,342	$	4	$	381	$	203,965

Fair Value, by Balance Sheet Grouping

The following is a reconciliation of our investments to the balance sheet classifications at December 31, 2016 and 2015:

In thousands	2016		2015
Cash equivalents	$	2,266	$	15,072
Short-term investments	180,849		188,893
Investments, at estimated fair value	$	183,115	$	203,965

Investments Classified by Contractual Maturity Date

The gross amortized cost and estimated fair value of our investments at December 31, 2016, 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	$	112,164	$	112,058
Due after one year through five years	71,274		71,057
Total	$	183,438	$	183,115

Schedule of Temporary Impairment Losses, Investments

The following table provides the breakdown of the cash equivalents and investments with unrealized losses at December 31, 2016:

	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
Commercial paper	17,693		60						17,693		60
U.S. treasury bills and notes	$	18,463	$	7	$	—	$	—	$	18,463	$	7
Securities and obligations of U.S. government agencies	103,426		265		—		—		103,426		265
Total	$	139,582	$	332	$	—	$	—	$	139,582	$	332

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. corporate debt securities	$	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