Significant Accounting Policies (Details 7) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Allocation of stock-based compensation expense
Stock-based compensation expense	$ 2,034,000	$ 2,364,000	$ 6,761,000	$ 7,596,000
Non-vested stock option
Allocation of stock-based compensation expense
Unrecognized estimated non-cash stock-based compensation expense	7,300,000		7,300,000
Weighted average period over which cost is expected to be recognized			1 year 2 months 12 days
RSUs
Allocation of stock-based compensation expense
Unrecognized estimated non-cash stock-based compensation expense	1,200,000		1,200,000
Weighted average period over which cost is expected to be recognized			3 years 3 months 18 days
Research and development
Allocation of stock-based compensation expense
Stock-based compensation expense	1,720,000	2,017,000	5,728,000	6,594,000
General and administrative
Allocation of stock-based compensation expense
Stock-based compensation expense	$ 314,000	$ 347,000	$ 1,033,000	$ 1,002,000