INVESTMENTS

Investments Available-for-Sale

Cash equivalents and investments by security type were as follows. The amounts presented exclude cash, but include investments classified as cash equivalents (in thousands):



	December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Money market funds	$	45,478	$	—	$	—		$	45,478
Commercial paper	199,647		—		—			199,647
Corporate bonds	179,336		18		(332		)	179,022
U.S. Treasury and government sponsored enterprises	16,295		—		(32		)	16,263
Total	$	440,756	$	18	$	(364	)	$	440,410



	December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Money market funds	$	71,457	$	—	$	—		$	71,457
Commercial paper	165,375		—		—			165,375
Corporate bonds	152,712		3		(308		)	152,407
U.S. Treasury and government sponsored enterprises	70,730		11		(14		)	70,727
Total	$	460,274	$	14	$	(322	)	$	459,966

Gains and losses on the sales of investments available-for-sale were nominal or zero during the years ended December 31, 2017, 2016 and 2015.

The fair value and gross unrealized losses of investments available-for-sale in an unrealized loss position were as follows (in thousands):



	December 31, 2017
	In an Unrealized Loss Position Less than 12 Months					In an Unrealized Loss Position 12 Months or Greater					Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Corporate bonds	$	140,746	$	(296	)	$	20,047	$	(36	)	$	160,793	$	(332	)
U.S. Treasury and government sponsored enterprises	13,611		(23		)	2,651		(9		)	16,262		(32		)
Total	$	154,357	$	(319	)	$	22,698	$	(45	)	$	177,055	$	(364	)



	December 31, 2016
	In an Unrealized Loss Position Less than 12 Months					In an Unrealized Loss Position 12 Months or Greater					Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Corporate bonds	$	140,559	$	(305	)	$	3,001	$	(3	)	$	143,560	$	(308	)
U.S. Treasury and government sponsored enterprises	27,657		(14		)	—		—			27,657		(14		)
Commercial paper⁽¹⁾	998		—			—		—			998		—
Total	$	169,214	$	(319	)	$	3,001	$	(3	)	$	172,215	$	(322	)

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(1)	Gross unrealized losses on commercial paper were less than $1 thousand.

There were 134 and 86 investments in an unrealized loss position as of December 31, 2017 and 2016, respectively. During the years ended December 31, 2017, 2016 and 2015 we did not record any other-than-temporary impairment charges on our available-for-sale securities. Based upon our quarterly impairment review, we determined that the unrealized losses were not attributed to credit risk, but were primarily associated with changes in interest rates. Based on the scheduled maturities of our investments and our determination that it was more likely than not that we will hold these investments for a period of time sufficient for a recovery of our cost basis, we concluded that the unrealized losses in our investment securities were not other-than-temporary.

The fair value of cash equivalents and investments by contractual maturity were as follows (in thousands):



	December 31,
	2017		2016
Maturing in one year or less	$	377,155	$	404,365
Maturing after one year through five years	63,255		55,601
Total	$	440,410	$	459,966

Cash is excluded from the table above. The classification of certain restricted investments was dependent upon the term of the underlying restriction on the asset and not the maturity date of the investment. As a result, certain investments with contractual maturities within one year were classified as long-term restricted cash and investments.

As of December 31, 2016, we were required to maintain compensating balances of $81.6 million in connection with our term loan payable to Silicon Valley Bank, which was included in short-term investments on the accompanying Consolidated Balance Sheet; as a result of our repayment of the term loan, the compensating balance requirement was terminated in March 2017.

Other Cost Method Equity Investments

During the years ended December 31, 2017 and 2016 we recognized gains of $3.0 million and $2.5 million, respectively, related to the August 2016 sale of our 9% interest in Akarna Therapeutics, Ltd. (“Akarna”) to Allergan Holdco UK Limited (“Allergan”). We acquired our interest in Akarna in 2015 in exchange for intellectual property rights related to the Exelixis discovered compound XL335. The gain on sale was included in Other expenses, net on the accompanying Consolidated Statements of Operations. We are eligible to earn additional such gains in the future as Allergan continues its development of XL335. The gain on sale of other cost method equity investments was nominal during the year ended December 31, 2015.