FAIR VALUE DISCLOSURE (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets measured and recorded at fair value	$ 148,477	$ 108,651
US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Short-term investments, at fair value	24,383
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Short-term investments, at fair value	118,323	60,878
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents, at fair value	2,771	47,773
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents, at fair value	3,000
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets measured and recorded at fair value	2,771	47,773
Level 1 | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Short-term investments, at fair value	0
Level 1 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Short-term investments, at fair value	0	0
Level 1 | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents, at fair value	2,771	47,773
Level 1 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents, at fair value	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets measured and recorded at fair value	145,706	60,878
Level 2 | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Short-term investments, at fair value	24,383
Level 2 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Short-term investments, at fair value	118,323	60,878
Level 2 | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents, at fair value	0	0
Level 2 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents, at fair value	3,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total assets measured and recorded at fair value	0	0
Level 3 | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Short-term investments, at fair value	0
Level 3 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Short-term investments, at fair value	0	0
Level 3 | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents, at fair value	0	0
Level 3 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents, at fair value	$ 0