Consolidated Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (7,572)	$ (6,885)
Changes in unrealized gain / (loss) on available-for-sale securities	9	(1)
Comprehensive loss	$ (7,563)	$ (6,886)