INVESTMENTS (Tables)

6 Months Ended

Jun. 30, 2018

Investments Schedule [Abstract]

Investments

Investments consist of the following (in thousands):

	June 30, 2018		December 31, 2017
Commercial paper	$	37,157	$	75,362
Corporate debt securities		543,648		414,815
Securities of government sponsored entities		10,901		18,401
Total investments	$	591,706	$	508,578

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
June 30, 2018:
Classified as current assets:
Commercial paper	Less than 1	$	37,211	$	—	$	(54	)	$	37,157
Corporate debt securities	Less than 1		300,451		—		(1,243	)		299,208
Securities of government-sponsored entities	Less than 1		6,000		—		(47	)		5,953
Total short-term available-for-sale securities		$	343,662	$	—	$	(1,344	)	$	342,318
Classified as non-current assets:
Corporate debt securities	1 to 2	$	245,850	$	—	$	(1,410	)	$	244,440
Securities of government-sponsored entities	1 to 2		5,003		—		(55	)		4,948
Total long-term available-for-sale securities		$	250,853	$	—	$	(1,465	)	$	249,388
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 June 30, 2018 and December 31, 2017, 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
June 30, 2018:
Commercial paper	$	37,157	$	(54	)	$	—	$	—		$	37,157	$	(54	)
Corporate debt securities		398,814		(1,803	)		138,935		(850	)		537,749		(2,653	)
Securities of government-sponsored entities		10,901		(102	)		—		—			10,901		(102	)
Total	$	446,872	$	(1,959	)	$	138,935	$	(850	)	$	585,807	$	(2,809	)
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	)