Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2012

Stock-Based Compensation [Abstract]

Stock-based compensation expenses

	Three months ended September 30,				Nine months ended September 30,
	2012		2011		2012		2011
Costs and expenses:
Research and development	$	774	$	975	$	2,195	$	2,786
General and administrative		630		1,077		1,816		3,196
Total stock-based compensation expense	$	1,404	$	2,052	$	4,011	$	5,982