Note 4 — Investments

At December 31, 2015 and 2014 the amortized cost and fair value of marketable securities were as follows:

			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
	(in thousands)
December 31, 2015
U.S. treasuries	$	94,935	$	6	$	(23	)	$	94,918
Government agency securities	12,985		3		—			12,988
Corporate debt	8,144		1		(1		)	8,144

Total available-for-sale securities	$	116,064	$	10	$	(24	)	$	116,050


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

Available-for-sale securities in a loss position at December 31, 2015 and 2014 were as follows:

	December 31, 2015					December 31, 2014
			Gross					Gross
	Estimated		Unrealized			Estimated		Unrealized
	Fair Value		Losses			Fair Value		Losses
	(in thousands)
U.S. treasuries	$	64,922	$	(23	)	$	35,001	$	(6	)
Corporate debt	3,353		(1		)	13,069		(6		)

Total	$	68,275	$	(24	)	$	48,070	$	(12	)

At December 31, 2015 and 2014, there were no short-term investments that had been in a continuous loss position for more than 12 months.

The maturities of securities classified as available-for-sale at December 31, 2015 were all due in one year or less. 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. There were minimal realized gains for the years ended December 31, 2015, 2014, and 2013, which were included in “Other, net” in the Consolidated Statements of Operations. There were no realized losses in any of the three years.

Restricted Cash

The Company did not have any restricted cash at December 31, 2015. At December 31, 2014 the restricted cash balance was $0.5 million, which served 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 has an ownership interest of less than 20% in a non-marketable investment. The Company does not exert significant influence over the investee and therefore the investment is carried at cost. Additional investments of $1.6 million were made during the year ended December 31, 2015, increasing the carrying value of the investment from $19.4 million at December 31, 2014 to $21.0 million at December 31, 2015. The Company’s ownership interest and participating rights have not substantively changed. Therefore, the Company continues to carry the investment at cost. The investment is included in “Other assets” on the Consolidated Balance Sheet. The investment is subject to a periodic impairment review; as there are no open-market valuations, the impairment analysis requires 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, business valuation indications from recent rounds of financing, the likelihood of obtaining subsequent rounds of financing, and the impact of equity preferences held by the Company relative to other investors. 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.