FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 151,408	$ 129,770
Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	500	3,099
Estimate of Fair Value, Fair Value Disclosure [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	17,554	17,492
Estimate of Fair Value, Fair Value Disclosure [Member] | Corporate securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	133,354	109,179
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	17,554	17,492
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	17,554	17,492
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	133,854	112,278
Significant Other Observable Inputs (Level 2) [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	500	3,099
Significant Other Observable Inputs (Level 2) [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents	0	0
Significant Other Observable Inputs (Level 2) [Member] | Corporate securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 133,354	$ 109,179