MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS - Assets measured at fair value on a recurring basis (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 14,974	$ 14,327	$ 19,533	$ 11,095
Auction rate securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Auction rate securities-long term	1,787
Fair Value, Measurements, Recurring | Estimate of Fair Value, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	12,728	11,754
Total	117,395	128,026
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	12,728	11,754
Total	12,728	11,754
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Total	102,880	114,483
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Total	1,787	1,789
Fair Value, Measurements, Recurring | Corporate debt securities-short term & long term | Estimate of Fair Value, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities-short term	72,134	64,944
Debt securities-long term	30,746	49,539
Fair Value, Measurements, Recurring | Corporate debt securities-short term & long term | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities-short term
Debt securities-long term
Fair Value, Measurements, Recurring | Corporate debt securities-short term & long term | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities-short term	72,134	64,944
Debt securities-long term	30,746	49,539
Fair Value, Measurements, Recurring | Corporate debt securities-short term & long term | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities-short term
Debt securities-long term
Fair Value, Measurements, Recurring | Auction rate securities | Estimate of Fair Value, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Auction rate securities-long term	1,787	1,789
Fair Value, Measurements, Recurring | Auction rate securities | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Auction rate securities-long term
Fair Value, Measurements, Recurring | Auction rate securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Auction rate securities-long term
Fair Value, Measurements, Recurring | Auction rate securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Auction rate securities-long term	$ 1,787	$ 1,789