Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Amounts Reclassified Out Of Accumulated Other Comprehensive Income Loss [Abstract]
Net loss	$ (31,238)	$ (22,899)	$ (7,283)
Unrealized (losses) gains on available-for-sale and long-term marketable securities:
Unrealized (losses) gains arising during holding period	(236)	257	108
Less: Reversal of unrealized gains in accumulated other comprehensive income upon the sale of long-term marketable securities		(590)
Other comprehensive (loss) income	(236)	(333)	108
Total comprehensive loss	$ (31,474)	$ (23,232)	$ (7,175)