Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2012

Stock-Based Compensation [Abstract]

Stock-based compensation expenses

	Three months ended June 30,				Six months ended June 30,
	2012		2011		2012		2011
Costs and expenses:
Research and development	$	646	$	900	$	1,421	$	1,811
General and administrative		578		1,066		1,186		2,118
Total stock-based compensation expense	$	1,224	$	1,966	$	2,607	$	3,929