SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Available-for-sale Investments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 137,050	$ 112,068
Gross Unrealized Gains	364	236
Gross Unrealized Losses	(7)	(26)
Estimated Fair Market Value	137,407	112,278
Investments due in less than 3 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,722	3,098
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Estimated Fair Market Value	3,723	3,099
Investments due in 4-12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	16,502	6,007
Gross Unrealized Gains	63	33
Gross Unrealized Losses	0	0
Estimated Fair Market Value	16,565	6,040
Investments due in more than 12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	116,826	102,963
Gross Unrealized Gains	300	202
Gross Unrealized Losses	(7)	(26)
Estimated Fair Market Value	117,119	103,139
Commercial paper [Member] | Investments due in less than 3 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,722	3,098
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Estimated Fair Market Value	3,723	3,099
Corporate securities [Member] | Investments due in 4-12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	16,502	6,007
Gross Unrealized Gains	63	33
Gross Unrealized Losses	0	0
Estimated Fair Market Value	16,565	6,040
Corporate securities [Member] | Investments due in more than 12 months [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	116,826	102,963
Gross Unrealized Gains	300	202
Gross Unrealized Losses	(7)	(26)
Estimated Fair Market Value	$ 117,119	$ 103,139