Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Amounts Reclassified Out Of Accumulated Other Comprehensive Income Loss [Abstract]
Net loss	$ (9,883)	$ (7,726)	$ (29,046)	$ (15,350)
Unrealized (losses) gains on available-for-sale and long-term marketable securities:
Unrealized (losses) gains arising during holding period	(65)	40	(178)	275
Less: Reversal of unrealized losses in accumulated other comprehensive loss upon the sale of long-term marketable securities included in investment and other income				(590)
Other comprehensive (loss) gain	(65)	40	(178)	(315)
Total comprehensive loss	$ (9,948)	$ (7,686)	$ (29,224)	$ (15,665)