MARKETABLE SECURITITES Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 130,654	$ 83,866
Gross Unrealized Gains	68	8
Gross Unrealized Losses	(49)	(105)
Estimated Fair Market Value	130,673	83,769
Investments due in less than 3 months:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,498	38,586
Gross Unrealized Gains	0	7
Gross Unrealized Losses	0	(10)
Estimated Fair Market Value	6,498	38,583
Investments due in 4-12 months:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	96,912	33,654
Gross Unrealized Gains	27	1
Gross Unrealized Losses	(7)	(36)
Estimated Fair Market Value	96,932	33,619
Investments due between 12 months and 5 years:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,244	11,626
Gross Unrealized Gains	41	0
Gross Unrealized Losses	(42)	(59)
Estimated Fair Market Value	27,243	11,567
Corporate securities | Investments due in less than 3 months:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,001	38,586
Gross Unrealized Gains	0	7
Gross Unrealized Losses	0	(10)
Estimated Fair Market Value	5,001	38,583
Corporate securities | Investments due in 4-12 months:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	51,558	33,654
Gross Unrealized Gains	27	1
Gross Unrealized Losses	(7)	(36)
Estimated Fair Market Value	51,578	33,619
Corporate securities | Investments due between 12 months and 5 years:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,244	11,626
Gross Unrealized Gains	41	0
Gross Unrealized Losses	(42)	(59)
Estimated Fair Market Value	27,243	$ 11,567
Commercial paper | Investments due in less than 3 months:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,497
Gross Unrealized Gains	0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	0
Estimated Fair Market Value	1,497
Commercial paper | Investments due in 4-12 months:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	45,354
Gross Unrealized Gains	0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	0
Estimated Fair Market Value	$ 45,354