Consolidated Statements of Comprehensive Loss (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Consolidated Statements of Comprehensive Loss [Abstract]
Net loss	$ (5,450)	$ (5,728)	$ (12,335)	$ (12,996)
Changes in unrealized loss on available-for-sale securities	(26)	(4)	(27)	(19)
Comprehensive loss	$ (5,476)	$ (5,732)	$ (12,362)	$ (13,015)