| Summary of Significant Accounting Policies | SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES PRINCIPLES OF CONSOLIDATION The accompanying consolidated financial statements include the accounts of Stillwater Mining Company, its wholly-owned subsidiaries and entities in which it holds a controlling interest (collectively referred to as the “Company”). All inter-company transactions and balances have been eliminated upon consolidation. CASH AND CASH EQUIVALENTS Cash and cash equivalents consist of all cash balances and all highly liquid investments purchased with an original maturity of three months or less. INVESTMENTS Investment securities at December 31, 2016 , and 2015 , consist of mutual funds, federal agency notes and commercial paper with stated maturities less than two years . All securities are reported at fair value. Unrealized holding gains and losses on available-for-sale securities are excluded from earnings and are reported as a separate component of other comprehensive income (loss) until realized. Realized gains and losses are based on the carrying value (cost, net of discounts or premiums) of the sold investment and recorded as a component of other income. A decline in the market value of any available-for-sale security below cost that is deemed to be other-than-temporary results in a reduction of the carrying amount of the security to fair value. The impairment is charged to earnings and a new cost basis for the security is established. The Company’s long-term investments in various junior exploration companies were originally recorded at cost due to less than 20% equity ownership interest and no significant Company control over the investees. A decline in the market value of these long-term investments that is deemed to be other-than-temporary will result in a reduction of the carrying amount of the investment to fair value. The impairment is charged to earnings and a new cost basis for the investment is established. RESTRICTED INVESTMENTS Restricted investments are amounts that have been pledged as collateral on outstanding undrawn letters of credit (associated with reclamation obligations). The Company reviews the letters of credit and the nature of the collateral annually and therefore restricted investments is classified as current. The restrictions on the balances lapse upon expiration of the letters of credit which currently have terms of one year or less. INVENTORIES Mined inventories are carried at the lower of current realizable value or average cost. Production costs include the costs of direct labor and materials, depletion, depreciation and amortization, and overhead costs relating to mining and processing activities. The value of recycled inventories is determined based on the acquisition costs of the recycled material and includes all inventoriable processing costs, including direct labor, direct materials, depreciation, transportation and third-party refining costs which relate to the processing activities. Materials and supplies inventories are valued at the lower of average cost or fair market value. RECEIVABLES Trade receivables and other receivable balances recorded in other current assets are reported at outstanding principal amounts, net of an allowance for doubtful accounts, if deemed necessary. Management evaluates the collectability of receivable account balances to determine the allowance, if any. Management considers the other party’s credit risk and financial condition, as well as current and projected economic and market conditions, in determining the amount of the allowance. Receivable balances are written off when management determines that the balance is uncollectable. The Company determined that no allowance against its receivable balances at December 31, 2016 and 2015 was necessary. MINERAL PROPERTIES AND MINE DEVELOPMENT Costs of acquiring mineral properties and mineral rights are capitalized as incurred. Prior to acquiring such mineral properties or mineral rights, the Company makes a preliminary evaluation to determine that the mineral property has significant potential to develop an economic ore body. The time between initial acquisition and full evaluation of a mineral property’s potential is variable and is determined by many factors including its location relative to existing infrastructure, stage of development, geological controls and relevant metal prices. When it has been determined that proven and probable ore reserves have been established in compliance with the SEC's Industry Guide 7, and a determination has been made to proceed toward commercial development, mining development costs incurred to develop the mineral property are capitalized. Mining exploration costs are expensed as incurred. If a mineable ore body is discovered, such costs are amortized when production begins using the units-of-production method based on the estimated quantities of recoverable metal. If no mineable ore body is discovered, such costs are expensed in the period in which it is determined the mineral property has no future economic value. Costs incurred to maintain assets on a standby basis are charged to operations. Costs of abandoned projects are charged to operations upon abandonment. Capitalized mine development costs are expenditures incurred to increase existing production, develop new ore bodies or develop mineral property substantially in advance of production. Capitalized mine development costs include a vertical shaft, multiple surface adits and underground infrastructure development including footwall laterals, ramps, rail and transportation, electrical and ventilation systems, shop facilities, material handling areas, ore handling facilities, dewatering and pumping facilities. These expenditures are capitalized and amortized over the life of the mine or over a shorter mining period, depending on the period benefited by those expenditures, using the units-of-production method. The Company utilizes Industry Guide 7 compliant total proven and probable ore reserves, measured in tons, as the basis for determining the life of mine and uses the ore reserves in the immediate and relevant vicinity as the basis for determining the shorter mining period. The Company calculates amortization of capitalized mine development costs in any vicinity by applying an amortization rate to the relevant current production. The amortization rates are each based upon a ratio of unamortized capitalized mine development costs to the related ore reserves. Capital development expenditures are added to the unamortized capitalized mine development costs and amortization rates are updated as the related assets are placed into service. In calculating the amortization rate, changes in ore reserves are accounted for as a prospective change in estimate. Ore reserves and the further benefit of capitalized mine development costs are determined based on management assumptions. Any significant changes in these assumptions, such as a change in the mine plan or a change in estimated proven and probable ore reserves could have a material effect on the expected period of benefit resulting in a potentially significant change in the amortization rate and / or the valuations of related assets. The Company’s proven ore reserves are generally expected to be extracted utilizing its existing mine development infrastructure. Additional capital expenditures will be required to access the Company’s estimated probable ore reserves. These anticipated capital expenditures are not included in the current calculation of depletion, depreciation and amortization. Expenditures incurred to sustain existing production and directly access specific ore reserve blocks or stopes provide benefit to ore reserve production over limited periods of time (secondary development) and are charged to operations as incurred. These costs include ramp and stope access excavations from the primary haulage levels (footwall laterals), stope material re-handling / laydown excavations, stope ore and waste pass excavations and chute installations, stope ventilation raise excavations and stope utility and pipe raise excavations. PROPERTY, PLANT AND EQUIPMENT Plant facilities and equipment are recorded at cost and depreciated using the straight-line method over estimated useful lives ranging from one to fifteen years. Interest is capitalized on expenditures related to major construction or development projects and is amortized using the same method as the related asset. Interest capitalization is discontinued when the asset is placed into operation or when development and construction cease. Maintenance and repairs are charged to costs of revenues as incurred. LEASES The Company classifies a lease as either capital or operating. All capital leases are depreciated over the shorter of the useful life of the asset or the lease term. ASSET IMPAIRMENT The Company reviews and evaluates its long-lived assets, including mineral properties and mine development, for impairment when events or changes in circumstances indicate that the related carrying amounts for such an asset may not be recoverable. For purposes of determining impairment, assets are grouped at the lowest level for which identifiable cash flows are largely independent of the cash flows of other groups of assets and liabilities. Impairment is considered to exist if the carrying amount of any long-lived asset or asset group is not recoverable and exceeds its fair value; the carrying value of a long-lived asset is considered not recoverable if it exceeds the sum of the undiscounted future cash flows expected to result from the use and eventual disposition of the asset or asset group. If impairment exists, the associated impairment loss to be recognized is the amount by which the carrying amount of the long-lived asset or asset group exceeds the fair value. In the Company’s case, the estimation of future cash flows takes into account estimates of recoverable ounces, prices for PGMs and other relevant metals (using twelve-quarter historical trailing prices and third-party projections of future prices, rather than prices at a single point in time, as indicators of longer-term future prices), any structural shifts in supply and demand or in competitive position, anticipated production levels, and future capital and reclamation expenditures, all based on life-of-mine plans and projections and measured as of the reporting date. The Company assesses, at least quarterly, whether there has been any event or change in circumstances that might indicate that the carrying value of capitalized mining costs and related property, plant and equipment, if any, may not be recoverable out of expected undiscounted future cash flows plus any estimated salvage value. In estimating the fair value of an asset or asset group, the Company takes into account various measurement alternatives, often engaging third-party advisors to assist in the process. Such alternatives will vary depending on the circumstances but could include information from recent sales of comparable assets, third-party professional appraisals, bona fide purchase offers, and valuations derived from discounted future cash flow models. Assumptions underlying future cash flows are subject to risks and uncertainties. Any differences between significant assumptions and market conditions such as PGM prices, lower than expected recoverable ounces, and / or the Company’s operating performance could have a material effect on the Company’s determination of ore reserves, or its ability to recover the carrying amounts of its long-lived assets resulting in potential additional impairment charges. FAIR VALUE OF FINANCIAL INSTRUMENTS The Company’s non-derivative financial instruments consist primarily of cash equivalents, trade receivables, payables, investments, convertible debentures and capital lease obligations. The carrying amounts of cash equivalents, trade receivables and payables approximate fair value due to their short maturities. The carrying amounts of investments approximate fair value based on market quotes. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants. A fair value hierarchy was established which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The fair value hierarchy distinguishes among three levels of inputs that may be utilized when measuring fair value: Level 1 inputs (using quoted prices in active markets for identical assets or liabilities), Level 2 inputs (using external inputs other than Level 1 prices such as quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability) and Level 3 inputs (unobservable inputs supported by little or no market activity and based on internal assumptions used to measure assets and liabilities). The classification of each financial asset or liability within the above hierarchy is determined based on the lowest level input that is significant to the fair value measurement. REVENUE RECOGNITION Revenue is comprised of Mine Production revenue, PGM Recycling revenue and other sales revenue. Mine Production revenue consists of the sales of palladium and platinum extracted by the Company’s mining operations, including any realized hedging gains or losses. Mine Production revenue also consists of the sales of by-products (rhodium, gold, silver, copper and nickel) extracted by mining operations. PGM Recycling revenue consists of the sales of recycled palladium, platinum and rhodium derived from spent catalytic materials, including any unrealized and realized hedging gains or losses. PGM recycling revenue also includes revenue from toll processing. Other sales revenue consists of sales of PGMs that are acquired periodically in the open market and simultaneously resold to third parties. Revenue is recognized when persuasive evidence of an arrangement exists, delivery has occurred either physically or through an irrevocable transfer of metals to customers’ accounts, the price is fixed or determinable, no related obligations remain and collectability is probable. Under the terms of sales contracts and purchase orders received from customers, the Company recognizes revenue when the product is in a refined and saleable form and title passes, which is typically when the product is transferred from the account of the Company to the account of the customer. Under certain of its sales agreements, the Company instructs a third-party refiner to transfer metal from the Company’s account to the customer’s account; at this point, the Company’s account at the third-party refinery is reduced and the purchaser’s account is increased by the number of ounces of metal sold. These transfers are irrevocable and the Company has no further responsibility for the delivery of the metals. Under other sales agreements, physical conveyance occurs by the Company arranging for shipment of metal from the third-party refinery to the purchaser. In these cases, revenue is recognized at the point when title passes contractually to the purchaser. Sales discounts are recognized when the related revenue is recorded. The Company classifies any sales discounts as a reduction in revenue. The Company recognizes revenue from its toll processing services at the time the contained metals are returned to the supplier at the third-party refinery. NONCONTROLLING INTEREST Noncontrolling interest is related to the sale of a 25% ownership interest in Stillwater Canada Inc during 2012. Noncontrolling interest is classified in the Company's Consolidated Statements of Comprehensive Income (Loss) as part of consolidated net income (loss) and the accumulated amount of noncontrolling interest in the Company's Consolidated Balance Sheets as a component of equity. In the fourth quarter of 2015, the Company repurchased the 25% ownership interest. RECLAMATION AND ENVIRONMENTAL COSTS The fair value of a liability for an asset retirement obligation is recognized in the period in which it is incurred if a reasonable estimate of fair value can be made. The fair value of the liability is added to the carrying amount of the associated asset and this additional carrying amount is depreciated over the life of the asset. The liability is accreted at the end of each period through charges to operating expense. If the obligation is settled for other than the carrying amount of the liability, the Company will recognize a gain or loss on settlement. Accounting for reclamation obligations requires management to make estimates for each mining operation of the future costs the Company will incur to complete final reclamation work required to comply with existing laws and regulations. Actual costs incurred in future periods could differ from amounts estimated. Additionally, future changes to environmental laws and regulations could increase the extent of reclamation and remediation work that the Company is required to perform. Any such increases in future costs could materially impact the amounts charged in future periods to operations for reclamation and remediation. INCOME TAXES The Company determines income taxes using the asset and liability method which results in the recognition of deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the carrying amounts and the tax bases of those assets and liabilities, as well as operating loss and tax credit carryforwards, using enacted tax rates in effect in the years in which the differences are expected to reverse. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. Deferred tax assets and liabilities are recorded on a jurisdictional basis. In assessing the realizability of U.S. and foreign deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. Each quarter, management considers the scheduled reversal of deferred tax liabilities, projected future taxable income, and tax planning strategies in making this assessment. A valuation allowance has been provided at December 31, 2016 , and 2015 , for the portion of the Company’s net deferred tax assets for which it is more likely than not that they will not be realized. STOCK-BASED COMPENSATION The Company estimates the fair value of performance-based restricted stock awards using a Monte Carlo simulation valuation model. The fair value of time-based restricted stock awards is determined by the market value of the underlying shares on the date of grant. Costs resulting from all share-based payment transactions are recognized in the financial statements over the respective vesting periods. All liability classified performance-based restricted stock awards are revalued each period with a charge to earnings. EARNINGS (LOSS) PER COMMON SHARE Basic earnings (loss) per share attributable to common stockholders is computed by dividing net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding during the period. Diluted earnings (loss) per share attributable to common stockholders reflects the potential dilution that could occur if the Company’s dilutive outstanding stock options or nonvested shares were exercised and the Company’s 1.875% and 1.75% Convertible Debentures were converted. Reported net income (loss) attributable to common stockholders is adjusted for the interest expense net of capitalized interest (including amortization expense of deferred debt and equity fees), the related income tax effect and the income (loss) attributable to the noncontrolling interest in the computation of basic and diluted earnings per share attributable to common stockholders. The Company currently has only one class of equity shares outstanding. COMPREHENSIVE INCOME (LOSS) Comprehensive income (loss) includes net income (loss), as well as other changes in stockholders’ equity that result from transactions and events other than those with stockholders. Other comprehensive income (loss) in 2016, 2015 and 2014 consisted of unrealized gains and losses related to available-for-sale marketable securities and deferred compensation. DEBT ISSUANCE COSTS Debt issuance costs are capitalized and amortized to interest expense using the effective interest method over the lives of the related debt agreements. On April 7, 2015, as part of their initiative to simplify and reduce complexity in the financial statements, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2015-03, Interest - Imputation, (Subtopic 835-30): Simplifying the Presentation of Debt Issuance. This ASU requires the debt issuance costs be presented in the balance sheet as a direct deduction from the carrying amount of the debt liability. Also, requiring retrospective application for all prior periods presented in the financial statements and a disclosure of the nature of and reason for the change in accounting principle, the transition method, a description of the prior-period information that has been retrospectively adjusted and the effect of the change on the financial statement line items. ASU 2015-03 is effective for financial statements issued for fiscal years beginning after December 31, 2015, and interim periods within those fiscal years. The Company adopted ASU 2015-03 in the first quarter of 2016 and reclassified Deferred debt issue costs against the related liability for all periods presented. Adoption of ASU 2015-03 had no financial impact other than to decrease the related liability. Prior to the adoption of ASU 2015-03, the balance reported at December 31, 2015 for total Long-term debt and capital lease obligations was $258.9 million , and after adoption and reclassification of Deferred debt issue costs of $3.8 million , the total adjusted balance reported at December 31, 2015 became $255.1 million . FOREIGN CURRENCY TRANSACTIONS The functional currency of the Company’s Canadian and South American subsidiaries is the U.S. dollar. Gains or losses resulting from transactions denominated in Canadian and South American currencies are included in Foreign currency transaction gain, net in the Company's Consolidated Statements of Comprehensive Income (Loss) . USE OF ESTIMATES The preparation of the Company’s consolidated financial statements in conformity with United States generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in these consolidated financial statements and accompanying notes. The more significant areas requiring the use of management’s estimates relate to mineral reserves, reclamation and environmental obligations, valuation allowance for deferred tax assets, useful lives utilized for depletion, depreciation, amortization and accretion calculations, future cash flows from long-lived assets, fair value of long-lived assets, and fair value of derivatives. Actual results could differ from these estimates. DEVELOPMENTS IN ACCOUNTING PRONOUNCEMENTS On May 28, 2014, the FASB issued Accounting Standards Update (ASU) 2014-09, Revenue from Contracts with Customers , which requires an entity to recognize the amount of revenue it expects to be entitled to for the transfer of promised goods or services to customers. The effective date of the new standard has been deferred by one year to January 1, 2018, and will replace most existing revenue recognition guidance in U.S. GAAP. The standard permits the use of either the retrospective or cumulative effect transition method. As of the date of this filing, the Company has not identified any revenue contracts that would require a material change in the Company's timing of revenue recognition. However, the Company continues to evaluate the impact that ASU 2014-09 will have on its consolidated financial position, results of operations, and cash flows and has not yet finalized the overall impact of the standard. The Company has not selected a transition method. Early application is not permitted. On July 22, 2015, as part of its initiative to simplify and reduce complexity in financial statements, the FASB issued ASU 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory. ASU 2015-11, changes the measurement principle for inventory from the lower of cost or market to the lower of cost and net realizable value. ASU 2015-11 is effective for financial statements issued for fiscal years beginning after December 15, 2016, and interim periods within those fiscal years. The Company does not expect ASU 2015-11 to have a material impact on its consolidated financial position, results of operations, or cash flows. The ASU requires prospective adoption and permits early adoption. On February 25, 2016, the FASB issued ASU 2016-02, Leases, (Topic 842) , which requires an entity that leases assets, with terms of more than 12 months, to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. ASU 2016-02 is effective for financial statements issued for fiscal years beginning after December 31, 2018, and interim periods within those fiscal years. The Company is currently evaluating the impact that ASU 2016-02 will have on its consolidated financial position, results of operations, and cash flows, but does not expect that the adoption will result in a significant increase in the Company's assets and liabilities given the limited current and anticipated lease activities. As of the date of this filing, the Company has not selected a transition method. Early adoption is permitted. On March 30, 2016, the FASB issued ASU 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employees Shared-Based Payment Accounting. The ASU will change several aspects within share based payments: (1) accounting for income taxes, (2) classification of excess tax benefits, (3) forfeitures, (4) minimum statutory tax withholding requirements, (5) classification of employee taxes paid when an employer withholds shares for tax-withholding purposes, (6) practical expedient - expected term, (7) intrinsic value, and (8) eliminating the indefinite deferral. ASU 2016-09 is effective for financial statements issued for fiscal years beginning after December 15, 2016, and interim periods within those fiscal years. The Company will adopt ASU 2016-09 in the first quarter of 2017. The Company is continuing to quantify the final effect that ASU 2016-09 will have on its consolidated financial position, results of operations, and cash flows. The Company chose not to early adopt. even though early adoption was permitted in any interim or annual period provided that the entire ASU was adopted. The Company anticipates the primary impact will be the excess tax benefits in the Company's income tax provision rather than in additional paid-in capital. ASU 2016-09 allows the Company to make a policy election as to whether it will include an estimate of awards expected to be forfeited or whether to account for forfeitures as they occur. The current forfeiture rate is immaterial, therefore, upon adoption the Company will account for the forfeitures as they occur. An additional amendment provides the Company with an option to make a policy change that will allow for withholding of maximum statutory rates in applicable jurisdictions without triggering liability accounting. |
