INVESTMENTS (Tables)

12 Months Ended

Dec. 31, 2017

Investments at December 31, 2017 and 2016 consisted of the following (in thousands):


	Years Ended December 31,
	2017		2016
Certificates of deposit	$	—	$	960
Commercial paper		75,362		49,245
Corporate debt securities		414,815		204,436
Securities of government-sponsored entities		18,401		12,932

Total investments	$	508,578	$	267,573

Summary of Investments Classified as Available-For-Sale Securities

The following is a summary of investments classified as available-for-sale securities (in thousands):


	Contractual Maturity (in years)		Amortized Cost		Gross Unrealized Gains(1)		Gross Unrealized Losses(1)			Aggregate Estimated Fair Value
December 31, 2016:
Classified as current assets:
Certificates of deposit		Less than 1	$	960	$	—	$	—		$	960
Commercial paper		Less than 1		49,280		3		(38	)		49,245
Corporate debt securities		Less than 1		168,548		3		(117	)		168,434
Securities of government-sponsored entities		Less than 1		5,448		—		(4	)		5,444

Total short-term available-for-sale securities			$	224,236	$	6	$	(159	)	$	224,083

Classified as non-current assets:
Corporate debt securities		1 to 2	$	36,149	$	—	$	(147	)	$	36,002
Securities of government-sponsored entities		1 to 2		7,506		—		(18	)		7,488

Total long-term available-for-sale securities			$	43,655	$	—	$	(165	)	$	43,490

December 31, 2017:
Classified as current assets:
Commercial paper		Less than 1	$	75,396	$	1	$	(35	)	$	75,362
Corporate debt securities		Less than 1		178,776		—		(400	)		178,376
Securities of government-sponsored entities		Less than 1		7,503		—		(24	)		7,479

Total short-term available-for-sale securities			$	261,675	$	1	$	(459	)	$	261,217

Classified as non-current assets:
Corporate debt securities		1 to 2	$	237,749	$	—	$	(1,310	)	$	236,439
Securities of government-sponsored entities		1 to 2		11,004		—		(82	)		10,922

Total long-term available-for-sale securities			$	248,753	$	—	$	(1,392	)	$	247,361

(1)	Unrealized gains and losses are included in other comprehensive loss.

Gross Unrealized Losses and Fair Value Available-For-Sale Investments in Unrealized Loss Position

The following table presents gross unrealized losses and fair value for those available-for-sale investments that were in an unrealized loss position as of December 31, 2017 and 2016, aggregated by investment category and length of time that individual securities have been in a continuous loss position (in thousands):


	Less Than 12 Months					12 Months or Greater					Total
	Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses
December 31, 2016:
Commercial paper	$	43,781	$	(38	)	$	—	$	—		$	43,781	$	(38	)
Corporate debt securities		185,243		(261	)		9,144		(3	)		194,387		(264	)
Securities of government-sponsored entities		12,932		(22	)		—		—			12,932		(22	)

Total	$	241,956	$	(321	)	$	9,144	$	(3	)	$	251,100	$	(324	)

December 31, 2017:
Commercial paper	$	62,602	$	(35	)	$	—	$	—		$	62,602	$	(35	)
Corporate debt securities		386,728		(1,660	)		28,087		(50	)		414,815		(1,710	)
Securities of government-sponsored entities		10,922		(82	)		7,479		(24	)		18,401		(106	)

Total	$	460,252	$	(1,777	)	$	35,566	$	(74	)	$	495,818	$	(1,851	)

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

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