Stock-Based Compensation (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Stock-based compensation expense
Stock-based compensation expense	$ 1,513	$ 1,591	$ 4,099	$ 2,807
Research And Development Expense [Member]
Stock-based compensation expense
Stock-based compensation expense	1,132	832	2,263	1,461
General And Administrative Expense [Member]
Stock-based compensation expense
Stock-based compensation expense	381	759	1,836	1,346
Employee And Directors Stock Options [Member]
Stock-based compensation expense
Stock-based compensation expense	1,471	1,526	4,000	2,657
Restricted Stock [Member]
Stock-based compensation expense
Stock-based compensation expense	$ 42	$ 65	$ 99	$ 150