EARNINGS PER SHARE (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Numerator:
Net loss	$ (11,956)	$ (14,784)	$ (14,031)	$ (23,138)	$ (16,346)	$ (15,745)	$ (8,296)	$ (11,894)	$ (63,909)	$ (52,281)	$ (43,328)
Denominator:
Weighted average shares of common stock outstanding									33,182	30,332	16,437
Net loss per share:
Basic and diluted net loss per share of common stock (in dollars per share)	$ (0.36)	$ (0.44)	$ (0.42)	$ (0.71)	$ (0.50)	$ (0.49)	$ (0.27)	$ (0.47)	$ (1.93)	$ (1.72)	$ (2.64)