Stock Option Plans (Tables)

12 Months Ended

Dec. 31, 2011

Stock Option Plans [Abstract]

Schedule Of Share-Based Compensation Expense

	Years ended December 31,
	2011		2010		2009
Research and development	$	9,820	$	8,230	$	7,312
General and administrative		10,164		6,100		4,537
Total	$	19,984	$	14,330	$	11,849

Schedule Of Stock Options Valuation Assumptions

	Stock option plans									Employee stock purchase plan
	Years ended December 31,									Years ended December 31,
	2011			2010			2009			2011			2010			2009
Risk-free interest rate		1.3	%		1.6	%		2.3	%		0.2	%		0.5	%		1.2	%
Expected lives in years		5.6			5.7			5.5			0.5			1.3			1.3
Expected dividends		0	%		0	%		0	%		0	%		0	%		0	%
Expected volatility		52	%		54	%		56	%		36	%		47	%		50	%

Schedule Of Stock Option Activity

	Shares			Weighted- average exercise price per share		Weighted-average remaining contractual term (in years)		Aggregate intrinsic value (in thousands)
Balances at December 31, 2010		12,739,831		$	9.94
Granted		2,828,125			16.45
Exercised		(1,669,489	)		7.38
Forfeited/expired		(143,899	)		12.73
Balances at December 31, 2011		13,754,568		$	11.55		7.19	$	72,667
Expected to vest		13,204,038		$	11.43		7.08	$	71,326
Options exercisable		7,823,456		$	9.60		5.96	$	55,664

Schedule Of Non-Vested Restricted Stock Units

	Share equivalent			Weighted- average grant date fair value
Nonvested RSUs
Nonvested at December 31, 2010		0		$	0
Changes during the period:
Granted		517,911			15.62
Vested		0			0
Forfeited		(6,744	)		15.33
Nonvested at December 31, 2011		511,167		$	15.62