SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011 Derivative financial instruments, stock warrant liability [Member]	Dec. 31, 2013 Convertible notes [Member]	Dec. 31, 2012 Convertible notes [Member]	Dec. 31, 2011 Convertible notes [Member]	Dec. 31, 2013 Fair value measured on a recurring basis Quoted prices in active markets (Level 1) [Member]	Dec. 31, 2012 Fair value measured on a recurring basis Quoted prices in active markets (Level 1) [Member]	Dec. 31, 2013 Fair value measured on a recurring basis Significant other observable inputs (Level 2) [Member]	Dec. 31, 2012 Fair value measured on a recurring basis Significant other observable inputs (Level 2) [Member]	Dec. 31, 2013 Fair value measured on a recurring basis Significant unobersvable inputs (Level 3) [Member]	Dec. 31, 2012 Fair value measured on a recurring basis Significant unobersvable inputs (Level 3) [Member]	Dec. 31, 2013 Total carrying value [Member]	Dec. 31, 2012 Total carrying value [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Cash equivalents							$ 7,600	$ 63,863	$ 0	$ 0	$ 0	$ 0	$ 7,600	$ 63,863
Short-term investments							202,024	154,018	0	0	0	4,000	202,024	158,018
Long-term investments							3,117	970	0	0	4,300	300	7,417	1,270
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of notes, beginning of year				4,300	4,300	0
Investments	0	4,300
Fair value of notes, end of year				4,300	4,300	0
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of stock warrant liability, beginning of year			10,660
Loss for period			(4,190)
Warrants exercised			14,850
Fair value of stock warrant liability, end of year			$ 0