Note 4 — Investments

At December 31, 2014 and 2013 the amortized cost and fair value of marketable securities were as follows:

			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
	(in thousands)
December 31, 2014
U.S. treasuries	$	81,506	$	27	$	(6	)	$	81,527
Corporate debt	39,031		20		(6		)	39,045
Total available-for-sale securities	$	120,537	$	47	$	(12	)	$	120,572

December 31, 2013
U.S. treasuries	$	130,956	$	22	$	(1	)	$	130,977
Government agency securities	61,004		9		—			61,013
Corporate debt	77,582		55		(36		)	77,601
Commercial paper	11,947		—		—			11,947
Total available-for-sale securities	$	281,489	$	86	$	(37	)	$	281,538

Available-for-sale securities in a loss position at December 31, 2014 and 2013 were as follows:

	December 31, 2014					December 31, 2013
	Estimated		Gross			Estimated		Gross
	Fair		Unrealized			Fair		Unrealized
	Value		Losses			Value		Losses
	(in thousands)
U.S. treasuries	$	35,001	$	(6	)	$	29,068	$	(1	)
Corporate debt	13,069		(6		)	37,654		(36		)
Total	$	48,070	$	(12	)	$	66,722	$	(37	)

As of December 31, 2014 and 2013, there were no short-term investments that had been in a continuous loss position for more than 12 months.

The contractual maturities of securities classified as available-for-sale at December 31, 2014 were as follows:

	December 31, 2014
			Estimated
	Amortized		Fair
	Cost		Value
	(in thousands)
Due in one year or less	$	74,710	$	74,718
Due after one year through two years	45,827		45,854
Total	$	120,537	$	120,572

Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Realized gains for the fiscal years ended December 31, 2014 and 2013 were $0.1 million in each period, and are included in “Other, net” in the Consolidated Statements of Operations. There were minimal realized gains for the year ended December 31, 2012 and no realized losses in any of the three years.

Restricted Cash

The total amount of restricted cash at December 31, 2014 and 2013 was $0.5 million and $2.7 million, respectively, which serves as collateral for bank guarantees that provide financial assurance that the Company will fulfill certain customer obligations. This cash is held in custody by the issuing bank, and is restricted as to withdrawal or use while the related bank guarantees are outstanding.

Cost Method Investment

The Company maintains certain investments in support of its strategic business objectives, including a non-marketable cost method investment. The Company’s ownership interest is less than 20% of the investee’s voting stock, and the Company does not exert significant influence, therefore the investment is recorded at cost. The carrying value of the investment was $19.4 million and $16.9 million at December 31, 2014 and 2013, respectively and is included in “Other assets” on the Consolidated Balance Sheet. The investment is subject to a periodic impairment review; however, there are no open-market valuations, and the impairment analysis requires significant judgment. The analysis includes assessments of the investee’s financial condition, the business outlook for its products and technology, its projected results and cash flow, the likelihood of obtaining subsequent rounds of financing, and the impact of any relevant contractual equity preferences held by the Company or others. Fair value of the investment is not estimated unless there are identified events or changes in circumstances that could have a significant adverse effect on the fair value of the investment. No such events or circumstances are present.