Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Contingency [Line Items]
Operating loss carryforwards	$ 205.9	$ 177.0
Research and development tax credit	5.7	3.8
Beginning year of net operating loss expiration	2019
Ending year of net operating loss expiration	2033
Deferred tax assets, percentage of valuation allowance	100.00%
Increase in deferred tax valuation allowance	14.5	13.6	9.5
Deferred tax asset, change in research credit carryforward, extension of credit	1.1	1.1
Federal statutory tax rate	34.00%	34.00%	34.00%
Share Based Compensation
Income Tax Contingency [Line Items]
Operating loss carryforwards	$ 3.2