SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Available-for-sale Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 96,729	$ 114,492
Gross Unrealized Gains	78	128
Gross Unrealized Losses	(11)	(45)
Estimated Fair Market Value	96,796	114,575
Investments due in less than 3 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,419
Gross Unrealized Gains	1
Gross Unrealized Losses	0
Estimated Fair Market Value	27,420
Investments due in 4-12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64,306	30,233
Gross Unrealized Gains	72	36
Gross Unrealized Losses	(11)	0
Estimated Fair Market Value	64,367	30,269
Investments due in more than 12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,004	84,259
Gross Unrealized Gains	5	92
Gross Unrealized Losses	0	(45)
Estimated Fair Market Value	5,009	84,306
Commercial paper [Member] | Investments due in less than 3 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,019
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Estimated Fair Market Value	18,019
Corporate securities [Member] | Investments due in less than 3 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,400
Gross Unrealized Gains	1
Gross Unrealized Losses	0
Estimated Fair Market Value	9,401
Corporate securities [Member] | Investments due in 4-12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64,306	30,233
Gross Unrealized Gains	72	36
Gross Unrealized Losses	(11)	0
Estimated Fair Market Value	64,367	30,269
Corporate securities [Member] | Investments due in more than 12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,004	84,259
Gross Unrealized Gains	5	92
Gross Unrealized Losses	0	(45)
Estimated Fair Market Value	$ 5,009	$ 84,306