Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) Share data in Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Segment Customer	Dec. 31, 2013 Customer	Dec. 31, 2012	Aug. 31, 2009	Nov. 30, 2010
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue	$ 376,000	$ 181,000
Long-term deferred revenue	100,000	0
Revenue from government grants	0	0	91,000
Number of major customers representing outstanding trade receivables	1	2
Life of inventory	2 years
Protracted length of inventory	1 year
Inventory valuation reserves	100,000	400,000
Capitalized costs for enhancement of enterprise resource planning software system and other internal use software	1,800,000	0
Estimated useful life of intangible assets	10 years
Number of reportable segments	1
Impairment charges on long-lived assets	0	0	0
Unrecognized Tax Benefits	0	0
Period of warranty	1 year
Computer Software, Intangible Asset
Summary Of Significant Accounting Policies [Line Items]
Enterprise resource planning system, estimated useful life	5 years
2009 Unit Offering
Summary Of Significant Accounting Policies [Line Items]
Warrants to purchase an aggregate shares of common stock				2.4
2010 Unit Offering
Summary Of Significant Accounting Policies [Line Items]
Warrants to purchase an aggregate shares of common stock					3.7
Other income, net
Summary Of Significant Accounting Policies [Line Items]
Reclassified amortization of premium from purchase of debt securities	$ 200,000
Trade Accounts Receivable | Customer Concentration Risk
Summary Of Significant Accounting Policies [Line Items]
Cumulative outstanding trade receivables percentage by major customers	36.00%	48.00%
Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	5 years