6. Investments

The following table summarizes the Company’s cash equivalents and investments:

	September 30, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash equivalents:
Money market funds	$	42,490	$	—	$	—		$	42,490
Short-term investments:
Certificates of deposit	23,281		3		(12		)	23,272
U.S. treasury notes	36,524		14		(3		)	36,535
U.S. government agency securities	103,122		42		(10		)	103,154
Long-term investments:
Certificates of deposit	10,121		5		(18		)	10,108
U.S. treasury notes	20,554		8		(12		)	20,550
U.S. government agency securities	18,983		11		(6		)	18,988

Total	$	255,075	$	83	$	(61	)	$	255,097

	December 31, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash equivalents:
Money market funds	$	31,761	$	—	$	—		$	31,761
Short-term investments:
Certificates of deposit	19,774		—		(28		)	19,746
U.S treasury notes	12,620		—		(14		)	12,606
U.S. government agency securities	102,683		—		(110		)	102,573
Long-term investments:
Certificates of deposit	12,299		—		(42		)	12,257
U.S. treasury notes	22,553		—		(105		)	22,448
U.S. government agency securities	45,793		—		(183		)	45,610

Total	$	247,483	$	—	$	(482	)	$	247,001

At September 30, 2016, and December 31, 2015, remaining contractual maturities of available-for-sale investments classified as current on the balance sheet were less than 12 months and remaining contractual maturities of available-for-sale investments classified as long-term were less than two years.

During the three and nine months ended September 30, 2016, other income, net in the statements of operations includes interest income on available-for-sale investments of $0.7 million and $1.9 million, respectively, and expense for the amortization of premiums and discounts on investments of $0.3 million and $0.8 million, respectively. During the three and nine months ended September 30, 2015, other income, net in the statements of operations includes interest income on available-for-sale investments of $0.4 million and $0.9 million, respectively, and expense for the amortization of premiums and discounts on investments of $0.2 million and $0.4 million, respectively.

There were no unrealized gains or losses on investments reclassified from accumulated other comprehensive income (loss) to other income in the Statements of Operations during the three and nine months ended September 30, 2016, and September 30, 2015.