Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2015
Summary of Significant Accounting Policies
Principles of Consolidation	Principles of Consolidation The accompanying unaudited interim consolidated financial statements include the financial statements of the Company and its wholly-owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.
Interim Financial Statements	Interim Financial Statements The accompanying unaudited interim consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (SEC). In the opinion of management, all adjustments, which consist solely of normal recurring adjustments, necessary to present fairly, in accordance with U.S. generally accepted accounting principles (GAAP), the financial position, results of operations and cash flows for all periods presented, have been made. The results of operations for the interim periods presented are not necessarily indicative of the results that may be expected for the full year. Certain information and footnote disclosures normally included in annual consolidated financial statements prepared in accordance with GAAP have been condensed or omitted. These unaudited interim consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K, filed for the fiscal year ended December 31, 2014. The information presented in the accompanying consolidated balance sheet as of December 31, 2014 has been derived from the Company’s December 31, 2014 audited consolidated financial statements. All other information has been derived from the unaudited interim consolidated financial statements of the Company.
Cash Equivalents	Cash Equivalents Cash equivalents consist of money market accounts with an initial term of less than three months. For purposes of the unaudited consolidated statements of cash flows, the Company considers all highly-liquid debt instruments with original maturities of three months or less to be cash equivalents. The Company’s cash and cash equivalents are deposited with financial institutions located in the U.S. and may at times exceed insured limits.
Revenue Recognition	Revenue Recognition The Company recognizes revenue under arrangements for products and services, which may include the sale of products and related services, including revenue from installation, service and maintenance, spare parts, hydrogen fueling services (which may include hydrogen supply as well as hydrogen fueling infrastructure) and leased units. The Company also recognizes revenue under research and development contracts, which are primarily cost reimbursement contracts associated with the development of PEM fuel cell technology. Products and Services The Company enters into revenue arrangements that may contain a combination of fuel cell systems and equipment, installation, service, maintenance, spare parts, hydrogen fueling and other support services. Revenue arrangements containing fuel cell systems and equipment may be sold, or leased to customers. For the above multiple deliverable arrangements, the Company accounts for each separate deliverable as a separate unit of accounting if the delivered item or items have value to the customer on a standalone basis. The Company considers a deliverable to have standalone value if the item is sold separately by us or another entity or if the item could be resold by the customer. The Company allocates revenue to each separate deliverable based on its relative selling price. For a majority of our deliverables, the Company determines relative selling prices using its best estimate of the selling price as vendor-specific objective evidence and third-party evidence is generally not available for the deliverables involved in its revenue arrangements due to a lack of a competitive environment in selling fuel cell technology. When determining estimated selling prices, the Company may consider the cost to produce the deliverable, the anticipated margin on that deliverable, the selling price and profit margin for similar products and services, the Company’s ongoing pricing strategy and policies, the value of any enhancements that have been built into the deliverable and the characteristics of the varying markets in which the deliverable is sold, as applicable. The Company determines estimated selling prices for deliverables in its arrangements based on the specific facts and circumstances of each arrangement and analyzes the estimated selling prices used for its allocation of consideration of each arrangement. Once relative selling prices are determined, the Company proportionately allocates the sale consideration to each element of the arrangement. The allocated sales consideration related to fuel cell systems and equipment, spare parts, and hydrogen infrastructure is recognized as revenue at shipment if title and risk of loss have passed to the customer, there is persuasive evidence of an arrangement, the sales price is fixed or determinable, collection of the related receivable is reasonably assured, and customer acceptance criteria, if any, have been successfully demonstrated. The allocated sales consideration related to installation, service, maintenance, and hydrogen molecule delivery is generally recognized as revenue when completed or on a straight-line basis over the term of the contract, as appropriate. The Company does not include a right of return on its products other than rights related to standard warranty provisions that permit repair or replacement of defective goods. The Company accrues for anticipated standard warranty costs at the same time that revenue is recognized for the related product. The Company has also sold extended warranty contracts that generally provide for a five to ten year warranty from the date of product installation. These types of contracts are accounted for as a separate deliverable, and accordingly, revenue generated from these transactions is deferred and recognized in income over the warranty period, generally on a straight-line basis. Additionally, the Company may enter into annual service and maintenance contracts that are billed monthly. Revenue generated from these transactions is recognized in income on a straight-line basis over the term of the contract. Costs are recognized as incurred over the term of the contract. Research and Development Contracts Contract accounting is used for research and development contract revenue. The Company generally shares in the cost of these programs with cost sharing percentages ranging from 30% to 50% of total project costs. Revenue from time and material contracts is recognized on the basis of labor hours expended plus other reimbursable contract costs incurred during the period. All allowable work performed through the end of each calendar quarter is billed, subject to limitations in the respective contracts. We expect to continue research and development contract work that is directly related to our current product development efforts. At September 30, 2015 and December 31, 2014, the Company had unbilled amounts from research and development contract revenue in the amount of approximately $0.5 million and $1.0 million, respectively, which is included in other current assets in the accompanying unaudited consolidated balance sheets. Unbilled amounts are expected to be billed during the following quarter.
Common Stock Warrant Accounting	Common Stock Warrant Accounting The Company accounts for common stock warrants in accordance with applicable accounting guidance provided in Accounting Standards Codification (ASC) Subtopic 815-40, Derivatives and Hedging — Contracts in Entity’s Own Equity, as either derivative liabilities or as equity instruments depending on the specific terms of the warrant agreement. In compliance with applicable securities law, registered common stock warrants that require the issuance of registered shares upon exercise and do not sufficiently preclude an implied right to cash settlement are accounted for as derivative liabilities. We currently classify these derivative warrant liabilities on the accompanying unaudited consolidated balance sheets as a long-term liability, which is revalued at each balance sheet date subsequent to the initial issuance using the Black-Scholes pricing model. The Black-Scholes pricing model, which is based, in part, upon unobservable inputs for which there is little or no market data, requires the Company to develop its own assumptions. Changes in the fair value of the warrants are reflected in the accompanying unaudited consolidated statements of operations as change in fair value of common stock warrant liability.
Joint Venture	Joint Venture Through July 31, 2015, we were party to a joint venture with Axane, under the name HyPulsion. The principal purpose of HyPulsion is to develop and sell hydrogen fuel cell systems for the European material handling market. On July 31, 2015 we purchased all of Axane’s equity interest in HyPulsion and now hold 100% of such interests. See note 4 regarding the acquisition of the remaining ownership interest of HyPulsion. Prior to the acquisition of HyPulsion, the Company had a zero basis in its investment.
Use of Estimates	Use of Estimates The unaudited interim consolidated financial statements have been prepared in conformity with GAAP, which require management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Reclassifications	Reclassifications Reclassifications are made, whenever necessary, to prior period financial statements to conform to the current period presentation. These reclassifications did not impact the results of operations or net cash flows in the periods presented.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In July 2015, an accounting update was issued that changes inventory measurement from lower of cost or market to lower of cost and net realizable value. The new standard applies to inventory measured at first-in, first-out (FIFO) or average cost. This accounting update is effective for the reporting periods beginning after December 15, 2016, and interim periods within those years. We do not expect the adoption of this update to have a significant effect on our consolidated financial statements. In August 2014, an accounting update was issued relating to how management assesses conditions and events that could raise substantial doubt about an entity’s ability to continue as a going concern. This accounting update is effective for reporting periods ending after December 15, 2016, and for annual and interim periods thereafter. We do not expect the adoption of this update to have a significant effect on our consolidated financial statements. In June 2014, an accounting update was issued that replaces the existing revenue recognition framework regarding contracts with customers. In July 2015, the Financial Accounting Standards Board (FASB) announced a one year delay in the required adoption date from January 1, 2017 to January 1, 2018. We are evaluating the effect this update will have on our consolidated financial statements and have not yet selected a transition method.