Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jan. 01, 2007
Income Taxes [Line Items]
Provision for income taxes	$ 0	$ 0	$ 0
Deferred tax assets attributable to excess stock option benefits	9,390,000	5,522,000
Increase (decrease) in net valuation allowance of deferred tax asset	44,800,000	30,900,000
Gross unrecognized tax benefit	1,488,000	619,000	435,000	483,000	0
Unrecognized tax benefits, interest and penalties	0
Increase or decrease of unrecognized tax benefits	0
Options to purchase common stock
Income Taxes [Line Items]
Deferred tax assets attributable to excess stock option benefits	5,200,000
Internal Revenue Service (IRS)
Income Taxes [Line Items]
Net operating losses	234,400,000
Internal Revenue Service (IRS) | Minimum [Member]
Income Taxes [Line Items]
Net operating loss carryforwards, expiry date	2024
Internal Revenue Service (IRS) | Research Tax Credit Carryforward
Income Taxes [Line Items]
Research and development tax credit carryforwards	3,700,000
Internal Revenue Service (IRS) | Research Tax Credit Carryforward | Minimum [Member]
Income Taxes [Line Items]
Research and development tax credits, expiry date	2028
State and Local Jurisdiction
Income Taxes [Line Items]
Net operating losses	191,100,000
State and Local Jurisdiction | Minimum [Member]
Income Taxes [Line Items]
Net operating loss carryforwards, expiry date	2014
State and Local Jurisdiction | Research Tax Credit Carryforward
Income Taxes [Line Items]
Research and development tax credit carryforwards	2,200,000
Foreign Tax Authority
Income Taxes [Line Items]
Net operating losses	$ 10,500,000