MARKETABLE SECURITIES - Available for Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 192,442	$ 5,160
Unrealized Gains	8	4,499
Unrealized Losses	(651)	(103)
Aggregate Estimated Fair Value	191,799	9,556
Less than 1 year
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	75,363
Unrealized Gains	6
Unrealized Losses	(119)
Aggregate Estimated Fair Value	75,250
1 to 2 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	117,079
Unrealized Gains	2
Unrealized Losses	(532)
Aggregate Estimated Fair Value	116,549
Common Stock
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		5,160
Unrealized Gains		4,499
Unrealized Losses		(103)
Aggregate Estimated Fair Value		$ 9,556
Commercial paper \| Less than 1 year
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	31,899
Unrealized Gains	6
Unrealized Losses	(41)
Aggregate Estimated Fair Value	31,864
Corporate debt securities \| Less than 1 year
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	43,464
Unrealized Gains	0
Unrealized Losses	(78)
Aggregate Estimated Fair Value	43,386
Corporate debt securities \| 1 to 2 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	82,557
Unrealized Gains	0
Unrealized Losses	(396)
Aggregate Estimated Fair Value	82,161
Securities of government sponsored entities \| 1 to 2 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	34,522
Unrealized Gains	2
Unrealized Losses	(136)
Aggregate Estimated Fair Value	$ 34,388

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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-Publisher FASB
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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