STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Total	Class A Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Comprehensive Loss [Member]
Balance at Dec. 31, 2008	$ 421,514	$ 2	$ 78	$ 1,294,813	$ (873,265)	$ (114)
Balance (in shares) at Dec. 31, 2008		2,249	77,642
Increase (decrease) in stockholders' equity [Roll Forward]
Issuance of Common Stock in connection with exercise of stock options, net of shares tendered	9,270		1	9,269
Issuance of Common Stock in connection with exercise of stock options, net of shares tendered (in shares)			1,134
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution	1,391			1,391
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution (in shares)			81
Conversion of Class A Stock to Common Stock	0
Conversion of Class A Stock to Common Stock (in shares)		(4)	4
Stock-based compensation charges	31,259			31,259
Net loss	(67,830)				(67,830)		(67,830)
Change in net unrealized gain (loss) on marketable securities, net of tax effect	1,158					1,158	1,158
Balance at Dec. 31, 2009	396,762	2	79	1,336,732	(941,095)	1,044	(66,672)
Balance (in shares) at Dec. 31, 2009		2,245	78,861
Increase (decrease) in stockholders' equity [Roll Forward]
Issuance of Common Stock in a public offering, net of issuance costs	174,828		6	174,822
Issuance of Common Stock in a public offering, net of issuance costs (in shares)			6,325
Issuance of Common Stock in connection with exercise of stock options, net of shares tendered	21,464		2	21,462
Issuance of Common Stock in connection with exercise of stock options, net of shares tendered (in shares)			1,533
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution	2,867			2,867
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution (in shares)			111
Issuance of restricted Common Stock under Long-Term Incentive Plan	0
Issuance of restricted Common Stock under Long-Term Incentive Plan (in shares)			345
Conversion of Class A Stock to Common Stock	0
Conversion of Class A Stock to Common Stock (in shares)		(63)	63
Stock-based compensation charges	39,897			39,897
Net loss	(104,468)				(104,468)		(104,468)
Change in net unrealized gain (loss) on marketable securities, net of tax effect	(3,535)					(3,535)	(3,535)
Balance at Dec. 31, 2010	527,815	2	87	1,575,780	(1,045,563)	(2,491)	(108,003)
Balance (in shares) at Dec. 31, 2010		2,182	87,238
Increase (decrease) in stockholders' equity [Roll Forward]
Issuance of Common Stock in connection with exercise of stock options, net of shares tendered	21,175		4	21,171
Issuance of Common Stock in connection with exercise of stock options, net of shares tendered (in shares)			3,324
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution	6,979			6,979
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution (in shares)			92
Issuance of restricted Common Stock under Long-Term Incentive Plan	0
Issuance of restricted Common Stock under Long-Term Incentive Plan (in shares)			16
Restricted Common Stock tendered upon vesting in connection with employee tax obligations	(2,638)			(2,638)
Restricted Common Stock tendered upon vesting in connection with employee tax obligations (in shares)			(51)
Conversion of Class A Stock to Common Stock	0
Conversion of Class A Stock to Common Stock (in shares)		(73)	73
Stock-based compensation charges	56,609			56,609
Equity component of convertible senior notes, net of issuance costs				120,623
Purchase of convertible note hedges	(117,500)			(117,500)
Issuance of warrants in connection with issuance of convertible senior notes	93,800			93,800
Net loss	(221,760)				(221,760)		(221,760)
Change in net unrealized gain (loss) on marketable securities, net of tax effect	629					629	629
Balance at Dec. 31, 2011	$ 485,732	$ 2	$ 91	$ 1,754,824	$ (1,267,323)	$ (1,862)	$ (221,131)
Balance (in shares) at Dec. 31, 2011		2,109	90,692