SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Short Term and Long Term Investments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accounting Policies [Abstract]
Weighted average interest rate on investments	1.66%	1.79%
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 82,789	$ 67,758
Gross Unrealized Gains	194	755
Gross Unrealized Losses	(202)	(1)
Estimated Fair Market Value	82,781	68,512
Investments due in less than 3 months [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	15,947	8,643
Gross Unrealized Gains	9	0
Gross Unrealized Losses	(1)	(1)
Estimated Fair Market Value	15,955	8,642
Investments due in 4-12 months [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	34,801	27,355
Gross Unrealized Gains	180	107
Gross Unrealized Losses	(23)	0
Estimated Fair Market Value	34,958	27,462
Investments due in more than 12 months [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	32,041	31,760
Gross Unrealized Gains	5	648
Gross Unrealized Losses	(178)	0
Estimated Fair Market Value	31,868	32,408
Commercial paper [Member] | Investments due in less than 3 months [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	9,849	7,135
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	9,849	7,135
Corporate securities [Member] | Investments due in less than 3 months [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	6,098	1,508
Gross Unrealized Gains	9	0
Gross Unrealized Losses	(1)	(1)
Estimated Fair Market Value	6,106	1,507
Corporate securities [Member] | Investments due in 4-12 months [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	24,801	21,255
Gross Unrealized Gains	179	84
Gross Unrealized Losses	(23)	0
Estimated Fair Market Value	24,957	21,339
Corporate securities [Member] | Investments due in more than 12 months [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	32,041	31,760
Gross Unrealized Gains	5	648
Gross Unrealized Losses	(178)	0
Estimated Fair Market Value	31,868	32,408
Certificates of deposit [Member] | Investments due in 4-12 months [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	10,000
Gross Unrealized Gains	1
Gross Unrealized Losses	0
Estimated Fair Market Value	10,001
U.S. Government debt securities [Member] | Investments due in 4-12 months [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost		5,095
Gross Unrealized Gains		20
Gross Unrealized Losses		0
Estimated Fair Market Value		5,115
U.S. municipal securities [Member] | Investments due in 4-12 months [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost		1,005
Gross Unrealized Gains		3
Gross Unrealized Losses		0
Estimated Fair Market Value		$ 1,008