SHORT-TERM INVESTMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
SHORT-TERM INVESTMENTS
Amortized Cost	$ 604,211
Gross Unrealized Gains	23
Gross Unrealized Losses	(1,675)
Estimated Fair Value	602,559	$ 0
Corporate notes and bonds
SHORT-TERM INVESTMENTS
Amortized Cost	430,855
Gross Unrealized Gains	6
Gross Unrealized Losses	(1,591)
Estimated Fair Value	429,270
U.S. agency obligations
SHORT-TERM INVESTMENTS
Amortized Cost	68,343
Gross Unrealized Gains	7
Gross Unrealized Losses	(61)
Estimated Fair Value	68,289
U.S. treasury securities
SHORT-TERM INVESTMENTS
Amortized Cost	55,434
Gross Unrealized Gains	7
Gross Unrealized Losses	(5)
Estimated Fair Value	55,436
Commercial paper
SHORT-TERM INVESTMENTS
Amortized Cost	39,259
Gross Unrealized Losses	(17)
Estimated Fair Value	39,242
Certificate of deposit
SHORT-TERM INVESTMENTS
Amortized Cost	10,320
Gross Unrealized Gains	3
Gross Unrealized Losses	(1)
Estimated Fair Value	$ 10,322

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

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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

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

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

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-Name Accounting Standards Codification

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