INVESTMENTS (Tables)

9 Months Ended

Sep. 30, 2017

Investments Schedule [Abstract]

Investments

Investments consist of the following (in thousands):

	September 30, 2017		December 31, 2016
Certificates of deposit	$	240	$	960
Commercial paper		66,735		49,245
Corporate debt securities		363,012		204,436
Securities of government sponsored entities		23,471		12,932
Total investments	$	453,458	$	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
September 30, 2017:
Classified as current assets:
Certificates of deposit		Less than 1	$	240	$	—	$	—		$	240
Commercial paper		Less than 1		66,759		—		(24	)		66,735
Corporate debt securities		Less than 1		163,870		3		(131	)		163,742
Securities of government-sponsored entities		Less than 1		12,503		—		(21	)		12,482
Total short-term available-for-sale securities			$	243,372	$	3	$	(176	)	$	243,199
Classified as non-current assets:
Corporate debt securities		1 to 2	$	199,615	$	—	$	(345	)	$	199,270
Securities of government-sponsored entities		1 to 2		11,005		—		(16	)		10,989
Total long-term available-for-sale securities			$	210,620	$	—	$	(361	)	$	210,259
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

(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 September 30, 2017 and December 31, 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
September 30, 2017:
Commercial paper	$	66,735	$	(24	)	$	—	$	—		$	66,735	$	(24	)
Corporate debt securities		325,223		(463	)		14,298		(13	)		339,521		(476	)
Securities of government-sponsored entities		15,988		(17	)		7,483		(20	)		23,471		(37	)
Total	$	407,946	$	(504	)	$	21,781	$	(33	)	$	429,727	$	(537	)
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	)