Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets:
Net operating loss carryforwards	$ 391,385	$ 351,354
Research and other credits	61,707	52,769
Deferred revenue	35,588	39,521
Sale of future royalties	28,057	39,750
Stock-based compensation	25,962	23,746
Capitalized research expenses	17,687	7,192
Reserves and accruals	14,685	8,776
Property and equipment	8,580	8,482
Other	2,539	2,773
Deferred tax assets before valuation allowance	586,190	534,363
Valuation allowance for deferred tax assets	(586,040)	(534,268)
Total deferred tax assets	150	95
Total deferred tax liabilities
Net deferred tax assets	$ 150	$ 95