SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Available-for-sale Investments) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 111,967	$ 31,627
Gross Unrealized Gains	122	139
Gross Unrealized Losses	(47)	0
Estimated Fair Market Value	112,042	31,766
Investments due in less than 3 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	15,884	1,500
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	0
Estimated Fair Market Value	15,884	1,501
Investments due in 4-12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7	24,127
Gross Unrealized Gains	0	83
Gross Unrealized Losses	0	0
Estimated Fair Market Value	7	24,210
Investments due in more than 12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	96,076	6,000
Gross Unrealized Gains	122	55
Gross Unrealized Losses	(47)	0
Estimated Fair Market Value	96,151	6,055
Commercial paper [Member] | Investments due in less than 3 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	9,991
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Estimated Fair Market Value	9,991
Corporate securities [Member] | Investments due in less than 3 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	5,893	1,500
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	0
Estimated Fair Market Value	5,893	1,501
Corporate securities [Member] | Investments due in 4-12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7	24,127
Gross Unrealized Gains	0	83
Gross Unrealized Losses	0	0
Estimated Fair Market Value	7	24,210
Corporate securities [Member] | Investments due in more than 12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	96,076	6,000
Gross Unrealized Gains	122	55
Gross Unrealized Losses	(47)	0
Estimated Fair Market Value	$ 96,151	$ 6,055