FINANCIAL INSTRUMENTS (Details 2) - Level 2 - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value Measurements
Cost	$ 328,692	$ 136,683
Gross Unrealized Gains	24	19
Gross Unrealized Losses	(88)	(49)
Fair Value	328,628	136,653
Short-term Investments \| Asset-backed securities
Fair Value Measurements
Cost	69,984	9,012
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(15)	(2)
Fair Value	69,969	9,010
Short-term Investments \| Commercial paper
Fair Value Measurements
Cost	35,896	39,530
Gross Unrealized Gains	3	8
Gross Unrealized Losses	(1)	(15)
Fair Value	35,898	39,523
Short-term Investments \| Corporate bonds
Fair Value Measurements
Cost	222,812	88,141
Gross Unrealized Gains	21	11
Gross Unrealized Losses	(72)	(32)
Fair Value	$ 222,761	$ 88,120

This item represents the cost of debt 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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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