Stock-Based Compensation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Costs and expenses:
Total stock-based compensation expense	$ 1,329	$ 1,383
Research and development [Member]
Costs and expenses:
Total stock-based compensation expense	685	775
General and administrative [Member]
Costs and expenses:
Total stock-based compensation expense	$ 644	$ 608