Analysis of Deferred Tax Assets (Liabilities) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 94,170	$ 85,600
Difference in depreciation and amortization	2,492	2,524
Research and development tax credits	23,599	20,012
Stock compensation	9,036	4,424
Deferred rent	2,849	265
Deferred revenue	1,219	1,133
Other	208	169
Gross deferred tax assets	133,573	114,127
Valuation allowance	(133,573)	(114,127)
Net deferred tax asset