STATEMENTS OF COMPREHENSIVE LOSS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
STATEMENTS OF COMPREHENSIVE LOSS [Abstract]
Net loss	$ (51,983)	$ (28,507)	$ (19,364)
Other comprehensive income (loss):
Net unrealized gains (losses) on investments available-for-sale	186	(402)	60
Foreign currency translation adjustment	223
Other comprehensive income (loss)	409	(402)	60
Comprehensive loss	$ (51,574)	$ (28,909)	$ (19,304)