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Significant Accounting Policies (Details 5) (USD $)	3 Months Ended		9 Months Ended
Significant Accounting Policies (Details 5) (USD $)	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Y D entity count	Sep. 30, 2010
Allocation of stock-based compensation expense
Stock-based compensation expense related to employee and non-employee stock options and the ESPP	$ 2,364,000	$ 2,960,000	$ 7,596,000	$ 9,447,000
Unrecognized compensation cost
Unrecognized compensation cost related to non-vested stock-based compensation plans	9,700,000		9,700,000
Weighted average period over which cost is expected to be recognized (in years)			1.3
Research and development
Allocation of stock-based compensation expense
Stock-based compensation expense related to employee and non-employee stock options and the ESPP	2,017,000	2,476,000	6,594,000	7,912,000
General and administrative
Allocation of stock-based compensation expense
Stock-based compensation expense related to employee and non-employee stock options and the ESPP	$ 347,000	$ 484,000	$ 1,002,000	$ 1,535,000

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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