Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Net operating loss carryforwards	$ 102,819	$ 46,230
Research and development credits	17,443	12,405
AMT credits	788	788
Foreign tax credits	3,196	3,196
Capitalized research and development and start-up costs	16,102	3,974
Deferred revenue	30,776	53,485
Deferred compensation	24,804	21,855
Intangible assets	2,540	4,302
Partnership interest	7,118	5,338
Other	4,173	2,850
Total deferred tax assets	209,759	154,423
Deferred tax liabilities:
Intangible assets	(38)	(91)
Unrealized gain on available-for-sale securities	(10,572)
Gain on issuance of stock by Regulus	(6,466)
Deferred tax asset valuation allowance	(192,721)	(154,423)
Net deferred tax liability	$ (38)	$ (91)