CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, except Share data	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2009	$ 177,965	$ 418	$ 476,663	$ 716	$ (299,832)
Beginning Balance (in shares) at Dec. 31, 2009		41,837,427
Exercise of common stock options (in shares)		227,970
Exercise of common stock options	1,733	2	1,731
Issuance of common stock under other types of equity plans (in shares)		164,656
Issuance of common stock under other types of equity plans	2,425	2	2,423
Issuance of restricted stock, net of cancellations and tax withholdings (in shares)		113,370
Issuance of restricted stock, net of cancellations and tax withholdings		1	(1)
Stock-based compensation expense	19,118		19,118
Foreign currency translation	(29)			(29)
Joint venture stock-based compensation (Regulus Therapeutics Inc.)	289		289
Tax benefit from stock-based compensation	220		220
Other comprehensive income	27			27
Net loss	(43,515)				(43,515)
Ending Balance at Dec. 31, 2010	158,233	423	500,443	714	(343,347)
Ending Balance (in shares) at Dec. 31, 2010		42,343,423
Exercise of common stock options (in shares)		16,800
Exercise of common stock options	103		103
Issuance of common stock under other types of equity plans (in shares)		124,815
Issuance of common stock under other types of equity plans	1,023	2	1,021
Issuance of restricted stock, net of cancellations and tax withholdings (in shares)		236,904
Issuance of restricted stock, net of cancellations and tax withholdings		2	(2)
Stock-based compensation expense	16,676		16,676
Joint venture stock-based compensation (Regulus Therapeutics Inc.)	370		370
Tax benefit from stock-based compensation	120		120
Other comprehensive income	(879)			(879)
Net loss	(57,649)				(57,649)
Ending Balance at Dec. 31, 2011	117,997	427	518,731	(165)	(400,996)
Ending Balance (in shares) at Dec. 31, 2011		42,721,942
Exercise of common stock options (in shares)	661,909	661,909
Exercise of common stock options	6,402	7	6,395
Issuance of common stock under other types of equity plans (in shares)		97,459
Issuance of common stock under other types of equity plans	879	1	878
Issuance of restricted stock, net of cancellations and tax withholdings (in shares)		383,626
Issuance of restricted stock, net of cancellations and tax withholdings	(519)	4	(523)
Issuance of common stock, net of offering costs (in shares)		8,625,000
Issuance of common stock, net of offering costs	86,800	86	86,714
Stock-based compensation expense	12,360		12,360
Joint venture stock-based compensation (Regulus Therapeutics Inc.)	321		321
Other comprehensive income	15,827			15,827
Net loss	(106,014)				(106,014)
Ending Balance at Dec. 31, 2012	$ 134,053	$ 525	$ 624,876	$ 15,662	$ (507,010)
Ending Balance (in shares) at Dec. 31, 2012		52,489,936