MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS

At September 30, 2016, the Company’s noncurrent restricted cash and available for sale investments totaling $122.4 million, includes $54.0 million of available for sale marketable securities and $68.4 million of cash. At December 31, 2015, the Company’s noncurrent restricted cash and available for sale investments totaling $101.8 million, includes $63.1 million of available for sale marketable securities and $38.7 million of cash. The Company’s restricted investments within WSE-related assets include $2.3 million of certificates of deposit as of September 30, 2016 and December 31, 2015. The available for sale marketable securities as of September 30, 2016 and December 31, 2015 consist of the following (in thousands):



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
September 30, 2016:
U.S. treasuries	$	53,376	$	152	$	(12	)	$	53,516
Mutual funds	500		9		—			509
Total investments	$	53,876	$	161	$	(12	)	$	54,025
December 31, 2015:
U.S. treasuries	$	64,226	$	9	$	(144	)	$	64,091
Mutual funds	500		4		—			504
Total investments	$	64,726	$	13	$	(144	)	$	64,595

There were no realized gains or losses for the nine months ended September 30, 2016 and 2015. As of September 30, 2016, all of the Company's U.S. treasuries had contractual maturity dates of less than three years.

As of September 30, 2016 and December 31, 2015, the Company had de minimis and $0.1 million in gross unrealized losses, respectively, in its U.S. Treasury securities. The fair value of the securities in an unrealized loss position represented approximately 28% and 81% of the total fair value of all U.S. Treasury securities as of September 30, 2016 and December 31, 2015, respectively. Unrealized losses are principally caused by changes in interest rates. In analyzing an issuer’s financial condition, the Company considers whether the securities are issued by the federal government or its agencies, whether downgrades by bond rating agencies have occurred, and industry analysts’ reports. As the Company has the ability and intent to hold debt securities until recovery, or for the foreseeable future as classified as available for sale, no decline was deemed to be other-than-temporary.

Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or a liability.

As a basis for considering such assumptions, the Company uses a three-tier value hierarchy, which prioritizes the inputs used in measuring fair value as follows:


•	Level I—observable inputs for identical assets or liabilities, such as quoted prices in active markets


•	Level II—inputs other than the quoted prices in active markets that are observable either directly or indirectly


•	Level III—unobservable inputs in which there is little or no market data, which requires the Company to develop its own assumptions

This hierarchy requires the Company to use observable market data when available and to minimize the use of unobservable inputs when determining fair value.

The following table summarizes the Company’s financial assets measured at fair value on a recurring basis (in thousands):



	Total Fair Value		Level I		Level II		Level III
September 30, 2016:
Certificates of deposit	$	2,319	$	2,319	$	—	$	—
U.S. treasuries	53,516		53,516		—		—
Mutual funds	509		509		—		—
Total	$	56,344	$	56,344	$	—	$	—
December 31, 2015:
Certificates of deposit	$	2,319	$	2,319	$	—	$	—
U.S. treasuries	64,091		64,091		—		—
Mutual funds	504		504		—		—
Total	$	66,914	$	66,914	$	—	$	—

There were no transfers between Level I and Level II assets during the nine months ended September 30, 2016 or the year ended December 31, 2015.

As of September 30, 2016 and December 31, 2015, certificates of deposit were held by domestic financial institutions, which are presented as restricted investments within WSE-related assets as described in Note 2.

The carrying value of the Company’s financial instruments not measured at fair value, including cash and cash equivalents, restricted cash, accounts receivable, accounts payable, approximates fair value due to their relatively short term nature. The fair value of these instruments would be categorized as Level II of the fair value hierarchy, with the exception of cash and cash equivalents, and restricted cash, which would be categorized as Level I.

At September 30, 2016 and December 31, 2015, the carrying value of the Company’s notes payable of $472.5 million and $499.6 million, respectively, approximated fair value. The estimated fair values of the Company’s notes payable are considered a Level II valuation in the hierarchy for fair value measurement and are based on a cash flow model discounted at market interest rates that considers the underlying risks of unsecured debt.