Summary of Significant Accounting Policies	3 Months Ended
Mar. 31, 2017
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, and are prepared in accordance with the requirements of the SEC for interim reporting. Certain amounts in the prior quarter’s condensed consolidated statements of operations have been reclassified to conform to the current quarter presentation. All significant intercompany activity has been eliminated in the preparation of the condensed consolidated financial statements. Effective January 1, 2017, the Company prospectively adopted certain requirements of Auditing Standards Update, or ASU, No. 2016-09 to classify cash flows related to excess tax benefits in operating activities without adjusting prior periods. In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments (consisting only of normal recurring adjustments) necessary to present fairly the consolidated financial position, results of operations, and cash flows of the Company. The Company’s subsidiaries include: (1) International Medication Systems, Limited, or IMS, (2) Armstrong Pharmaceuticals, Inc., or Armstrong, (3) Amphastar Nanjing Pharmaceuticals Inc., or ANP, (4) Nanjing Letop Fine Chemistry Co., Ltd., or Letop, (5) Amphastar France Pharmaceuticals, S.A.S., or AFP, (6) Amphastar UK Ltd., or AUK, and (7) International Medication Systems (UK) Limited, or IMS UK. Use of Estimates The preparation of consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ from those estimates. The principal accounting estimates include: determination of allowances for doubtful accounts and discounts, provision for chargebacks, liabilities for product returns, adjustment to cost for excess or unsellable inventory, impairment of long-lived and intangible assets and goodwill, self-insured claims, workers’ compensation liabilities, litigation reserves, stock price volatilities for share-based compensation expense, valuation allowances for deferred tax assets, and liabilities for uncertain income tax positions. Foreign Currency The functional currency of the Company, its domestic subsidiaries, its Chinese subsidiary, ANP, and its U.K. subsidiary, AUK, is the U.S. dollar, or USD. ANP maintains its books of record in Chinese Yuan. These books are remeasured into the functional currency of USD using the current or historical exchange rates. The resulting currency remeasurement adjustments and other transactional foreign currency exchange gains and losses are reflected in the Company’s statements of operations. The Company’s French subsidiary, AFP, Chinese subsidiary, Letop, and U.K. subsidiary, IMS UK maintain their books of record in Euros, Chinese Yuan, and Great Britain Pounds, respectively, which are the local currencies and have been determined to be their respective functional currencies. These books are translated into USD using average exchange rates during the period. Assets and liabilities are translated at the rate of exchange prevailing on the balance sheet date. Equity is translated at the prevailing rate of exchange at the date of the equity transactions. Translation adjustments are reflected in stockholders’ equity and are included as a component of other accumulated comprehensive income (loss). The unrealized gains or losses of intercompany foreign currency transactions that are of a long-term investment nature are reported in other accumulated comprehensive income (loss). The unrealized gains and losses of intercompany foreign currency transactions that are of a long-term investment nature for the three months ended March 31, 2017 and 2016 $0.5 million gain, and a $0.9 million gain, respectively. Additionally, the Company does not undertake hedging transactions to cover its foreign currency exposure. Comprehensive Income For the three months ended March 31, 2017 and 2016, the Company included its foreign currency translation as part of its comprehensive income. Financial Instruments The carrying amounts of cash and cash equivalents, short-term investments, restricted short-term investments, accounts receivable, accounts payable, accrued expenses, and short-term borrowings approximate fair value due to the short maturity of these items. A majority of the Company’s long-term obligations consist of variable rate debt, and their carrying value approximates fair value as the stated borrowing rates are comparable to rates currently offered to the Company for instruments with similar maturities. However, the Company has one fixed-rate, long-term mortgage for which the carrying value differs from the fair value and is not remeasured on a recurring basis (see Note 12). The Company at times enters into fixed interest rate swap contracts to exchange the variable interest rates for fixed interest rates without the exchange of the underlying notional debt amounts. Such interest rate swap contracts are recorded at their fair values. Deferred Income Taxes The Company utilizes the liability method of accounting for income taxes, under which deferred taxes are determined based on the temporary differences between the financial statements and the tax basis of assets and liabilities using enacted tax rates. A valuation allowance is recorded when it is more likely than not that the deferred tax assets will not be realized. Business Combinations If an acquired set of activities and assets is capable of being operated as a business consisting of inputs and processes from the viewpoint of a market participant, the asset acquired and liabilities assumed are a business. Business combinations are accounted for using the acquisition method of accounting, which requires an acquirer to recognize the assets acquired and the liabilities assumed at the acquisition date measured at their fair values as of that date. Fair value determinations are based on discounted cash flow analyses or other valuation techniques. In determining the fair value of the assets acquired and liabilities assumed in a material acquisition, the Company may utilize appraisals from third party valuation firms to determine fair values of some or all of the assets acquired and liabilities assumed, or may complete some or all of the valuations internally. In either case, the Company takes full responsibility for the determination of the fair value of the assets acquired and liabilities assumed. The value of goodwill reflects the excess of the fair value of the consideration conveyed to the seller over the fair value of the net assets received. Acquisition-related costs that the Company incurs to effect a business combination are expensed in the periods in which the costs are incurred. When the operations of the acquired businesses were not material to the Company's condensed consolidated financial statements, no pro forma presentation is disclosed. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board, or FASB, issued ASU No. 2014-09 which creates a single source of revenue guidance for companies in all industries. Subsequently, the FASB issued multiple updates. The new standard provides guidance for all revenue arising from contracts with customers and affects all entities that enter into contracts to provide goods or services to their customers, unless the contracts are within the scope of other accounting standards. It also provides a model for the measurement and recognition of gains and losses on the sale of certain nonfinancial assets. The guidance also requires expanded disclosures relating to the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Additionally, qualitative and quantitative disclosures are required regarding customer contracts, significant judgments and changes in judgments, and assets recognized from the costs to obtain or fulfill a contract. This guidance permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the cumulative catch-up transition method). Based on ASU No. 2015-14 issued in August 2015, this guidance will be effective for the Company in 2018, including interim periods within the year. The Company is in the process of evaluating the effect of the adoption on its condensed consolidated financial statements and is currently assessing its contracts with customers and sale of nonfinancial assets. The Company anticipates it will expand its consolidated financial statement disclosures in order to comply with the new guidance. The Company expects to select the modified retrospective transition method upon adoption. In February 2016, the FASB issued ASU No. 2016-02 that is aimed at making leasing activities more transparent and comparable, and which requires substantially all leases be recognized by lessees on their balance sheets as a right-of-use asset and corresponding lease liability, including leases currently accounted for as operating leases. This guidance will become effective for the Company’s interim and annual reporting periods during the year ending December 31, 2019, and all annual and interim reporting periods thereafter. Early adoption is permitted. The Company is required to use a modified retrospective approach for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements for the reporting periods in which the guidance is adopted. The Company is currently evaluating the impact that the adoption of this guidance will have on its consolidated financial statements and related disclosures. In March 2016, the FASB issued ASU No. 2016-09 that is aimed at improving the employee share-based payment accounting. The standard update simplifies the accounting for employee share-based payments and involves several aspects of the accounting for share-based transactions, including the potential timing of expenses, the income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. The Company adopted this guidance effective January 1, 2017. In June 2016, the FASB issued ASU No. 2016-13 that is aimed at providing financial statement users with more useful information about the expected credit losses on financial instruments and other commitments to extend credit. The standard update changes the impairment model for financial assets measured at amortized cost, requiring presentation at the net amount expected to be collected. The measurement of expected credit losses requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. Available-for-sale debt securities with unrealized losses will be recorded through an allowance for credit losses. The guidance is effective for the Company’s interim and annual reporting periods during the year ending December 31, 2020. Early adoption is permitted for annual periods after 2019. The Company will be required to apply the standard’s provisions as a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The Company is currently evaluating the impact that the adoption of this guidance will have on its consolidated financial statements and related disclosures. In August 2016, the FASB issued ASU No. 2016-15 that is aimed at addressing certain issues regarding classifications of certain cash receipts and cash payments on the statement of cash flows where diversity in practice was identified. The guidance is effective for the Company’s interim and annual reporting periods during the year ending December 31, 2018. Early adoption is permitted. The Company will be required to apply the guidance retrospectively in the first interim and annual periods in which the guidance is adopted. The Company does not believe that the adoption of this accounting guidance will have a material impact on the Company’s consolidated financial statements and related disclosures. In October 2016, the FASB issued ASU No. 2016-16 that requires an entity to recognize the income tax consequences of intra-entity transfer of an asset other than inventory when the transfer occurs. The guidance is effective for the Company's interim and annual reporting periods during the year ending December 31, 2018. Early adoption is permitted as of the beginning of an annual reporting period for which financial statements, interim or annual, have not been issued. The amendments will be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. The Company is currently evaluating the impact that the adoption of this guidance will have on its consolidated financial statements and related disclosures. In November 2016, the FASB issued ASU No. 2016-18 which requires entities to show the changes in the total of cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. As a result, the Company will no longer present transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. The guidance is effective for the Company's interim and annual reporting periods during the year ending December 31, 2018. Early adoption is permitted, including adoption in an interim period. The amendments will be applied using a retrospective transition method to each period presented. The Company will be required to apply the guidance retrospectively when adopted. The Company does not believe that the adoption of this accounting guidance will have a material impact on its consolidated financial statements and related disclosures. In January 2017, the FASB issued ASU No. 2017-01 which provides guidance to assist entities with evaluating when a set of transferred assets and activities is a business. Under the updated guidance, a set is not a business if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or a group of similar assets. If the threshold is not met, the update requires that, to be a business, the set must include, at a minimum, an input and a substantive process that together significantly contribute to the ability to create outputs. The definition of outputs was also aligned with Accounting Standard Codification, or ASC, 606 by focusing on revenue-generating activities. The guidance is effective for the Company’s interim and annual reporting periods during the year ending December 31, 2018, and prospectively applicable to any transactions occurring within the period of adoption. Early adoption is permitted. The Company is currently evaluating the impact that the adoption of this guidance will have on its consolidated financial statements and related disclosures. In January 2017, the FASB issued ASU No. 2017-04 which eliminates the requirement to calculate the implied fair value of goodwill. An entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The FASB also eliminated the requirements for any reporting unit with a zero or negative carrying amount to perform a qualitative assessment and, if it fails that qualitative test, to perform Step 2 of the goodwill impairment test. An entity is required to disclose the amount of goodwill allocated to each reporting unit with a zero or negative carrying amount of net assets. The guidance is effective for the Company’s interim and annual reporting periods during the year ending December 31, 2020, and applied on a prospective basis. Early adoption is permitted for interim and annual goodwill impairment testing dates after January 1, 2017. The Company is currently evaluating the impact that the adoption of this guidance will have on its consolidated financial statements and related disclosures.

2. Summary of Significant Accounting Policies

Basis of Presentation

The unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, and are prepared in accordance with the requirements of the SEC for interim reporting. Certain amounts in the prior quarter’s condensed consolidated statements of operations have been reclassified to conform to the current quarter presentation. All significant intercompany activity has been eliminated in the preparation of the condensed consolidated financial statements. Effective January 1, 2017, the Company prospectively adopted certain requirements of Auditing Standards Update, or ASU, No. 2016-09 to classify cash flows related to excess tax benefits in operating activities without adjusting prior periods. In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments (consisting only of normal recurring adjustments) necessary to present fairly the consolidated financial position, results of operations, and cash flows of the Company.

The Company’s subsidiaries include: (1) International Medication Systems, Limited, or IMS, (2) Armstrong Pharmaceuticals, Inc., or Armstrong, (3) Amphastar Nanjing Pharmaceuticals Inc., or ANP, (4) Nanjing Letop Fine Chemistry Co., Ltd., or Letop, (5) Amphastar France Pharmaceuticals, S.A.S., or AFP, (6) Amphastar UK Ltd., or AUK, and (7) International Medication Systems (UK) Limited, or IMS UK.

Use of Estimates

The preparation of consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ from those estimates. The principal accounting estimates include: determination of allowances for doubtful accounts and discounts, provision for chargebacks, liabilities for product returns, adjustment to cost for excess or unsellable inventory, impairment of long-lived and intangible assets and goodwill, self-insured claims, workers’ compensation liabilities, litigation reserves, stock price volatilities for share-based compensation expense, valuation allowances for deferred tax assets, and liabilities for uncertain income tax positions.

Foreign Currency

The functional currency of the Company, its domestic subsidiaries, its Chinese subsidiary, ANP, and its U.K. subsidiary, AUK, is the U.S. dollar, or USD. ANP maintains its books of record in Chinese Yuan. These books are remeasured into the functional currency of USD using the current or historical exchange rates. The resulting currency remeasurement adjustments and other transactional foreign currency exchange gains and losses are reflected in the Company’s statements of operations.

The Company’s French subsidiary, AFP, Chinese subsidiary, Letop, and U.K. subsidiary, IMS UK maintain their books of record in Euros, Chinese Yuan, and Great Britain Pounds, respectively, which are the local currencies and have been determined to be their respective functional currencies. These books are translated into USD using average exchange rates during the period. Assets and liabilities are translated at the rate of exchange prevailing on the balance sheet date. Equity is translated at the prevailing rate of exchange at the date of the equity transactions. Translation adjustments are reflected in stockholders’ equity and are included as a component of other accumulated comprehensive income (loss). The unrealized gains or losses of intercompany foreign currency transactions that are of a long-term investment nature are reported in other accumulated comprehensive income (loss). The unrealized gains and losses of intercompany foreign currency transactions that are of a long-term investment nature for the three months ended March 31, 2017 and 2016 $0.5 million gain, and a $0.9 million gain, respectively.

Additionally, the Company does not undertake hedging transactions to cover its foreign currency exposure.

Comprehensive Income

For the three months ended March 31, 2017 and 2016, the Company included its foreign currency translation as part of its comprehensive income.

Financial Instruments

The carrying amounts of cash and cash equivalents, short-term investments, restricted short-term investments, accounts receivable, accounts payable, accrued expenses, and short-term borrowings approximate fair value due to the short maturity of these items. A majority of the Company’s long-term obligations consist of variable rate debt, and their carrying value approximates fair value as the stated borrowing rates are comparable to rates currently offered to the Company for instruments with similar maturities. However, the Company has one fixed-rate, long-term mortgage for which the carrying value differs from the fair value and is not remeasured on a recurring basis (see Note 12). The Company at times enters into fixed interest rate swap contracts to exchange the variable interest rates for fixed interest rates without the exchange of the underlying notional debt amounts. Such interest rate swap contracts are recorded at their fair values.

Deferred Income Taxes

The Company utilizes the liability method of accounting for income taxes, under which deferred taxes are determined based on the temporary differences between the financial statements and the tax basis of assets and liabilities using enacted tax rates. A valuation allowance is recorded when it is more likely than not that the deferred tax assets will not be realized.

Business Combinations

If an acquired set of activities and assets is capable of being operated as a business consisting of inputs and processes from the viewpoint of a market participant, the asset acquired and liabilities assumed are a business. Business combinations are accounted for using the acquisition method of accounting, which requires an acquirer to recognize the assets acquired and the liabilities assumed at the acquisition date measured at their fair values as of that date. Fair value determinations are based on discounted cash flow analyses or other valuation techniques. In determining the fair value of the assets acquired and liabilities assumed in a material acquisition, the Company may utilize appraisals from third party valuation firms to determine fair values of some or all of the assets acquired and liabilities assumed, or may complete some or all of the valuations internally. In either case, the Company takes full responsibility for the determination of the fair value of the assets acquired and liabilities assumed. The value of goodwill reflects the excess of the fair value of the consideration conveyed to the seller over the fair value of the net assets received.

Acquisition-related costs that the Company incurs to effect a business combination are expensed in the periods in which the costs are incurred. When the operations of the acquired businesses were not material to the Company's condensed consolidated financial statements, no pro forma presentation is disclosed.

Recent Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board, or FASB, issued ASU No. 2014-09 which creates a single source of revenue guidance for companies in all industries. Subsequently, the FASB issued multiple updates. The new standard provides guidance for all revenue arising from contracts with customers and affects all entities that enter into contracts to provide goods or services to their customers, unless the contracts are within the scope of other accounting standards. It also provides a model for the measurement and recognition of gains and losses on the sale of certain nonfinancial assets. The guidance also requires expanded disclosures relating to the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Additionally, qualitative and quantitative disclosures are required regarding customer contracts, significant judgments and changes in judgments, and assets recognized from the costs to obtain or fulfill a contract. This guidance permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the cumulative catch-up transition method). Based on ASU No. 2015-14 issued in August 2015, this guidance will be effective for the Company in 2018, including interim periods within the year. The Company is in the process of evaluating the effect of the adoption on its condensed consolidated financial statements and is currently assessing its contracts with customers and sale of nonfinancial assets. The Company anticipates it will expand its consolidated financial statement disclosures in order to comply with the new guidance. The Company expects to select the modified retrospective transition method upon adoption.

In February 2016, the FASB issued ASU No. 2016-02 that is aimed at making leasing activities more transparent and comparable, and which requires substantially all leases be recognized by lessees on their balance sheets as a right-of-use asset and corresponding lease liability, including leases currently accounted for as operating leases. This guidance will become effective for the Company’s interim and annual reporting periods during the year ending December 31, 2019, and all annual and interim reporting periods thereafter. Early adoption is permitted. The Company is required to use a modified retrospective approach for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements for the reporting periods in which the guidance is adopted. The Company is currently evaluating the impact that the adoption of this guidance will have on its consolidated financial statements and related disclosures.

In March 2016, the FASB issued ASU No. 2016-09 that is aimed at improving the employee share-based payment accounting. The standard update simplifies the accounting for employee share-based payments and involves several aspects of the accounting for share-based transactions, including the potential timing of expenses, the income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. The Company adopted this guidance effective January 1, 2017.

In June 2016, the FASB issued ASU No. 2016-13 that is aimed at providing financial statement users with more useful information about the expected credit losses on financial instruments and other commitments to extend credit. The standard update changes the impairment model for financial assets measured at amortized cost, requiring presentation at the net amount expected to be collected. The measurement of expected credit losses requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. Available-for-sale debt securities with unrealized losses will be recorded through an allowance for credit losses. The guidance is effective for the Company’s interim and annual reporting periods during the year ending December 31, 2020. Early adoption is permitted for annual periods after 2019. The Company will be required to apply the standard’s provisions as a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The Company is currently evaluating the impact that the adoption of this guidance will have on its consolidated financial statements and related disclosures.

In August 2016, the FASB issued ASU No. 2016-15 that is aimed at addressing certain issues regarding classifications of certain cash receipts and cash payments on the statement of cash flows where diversity in practice was identified. The guidance is effective for the Company’s interim and annual reporting periods during the year ending December 31, 2018. Early adoption is permitted. The Company will be required to apply the guidance retrospectively in the first interim and annual periods in which the guidance is adopted. The Company does not believe that the adoption of this accounting guidance will have a material impact on the Company’s consolidated financial statements and related disclosures.

In October 2016, the FASB issued ASU No. 2016-16 that requires an entity to recognize the income tax consequences of intra-entity transfer of an asset other than inventory when the transfer occurs. The guidance is effective for the Company's interim and annual reporting periods during the year ending December 31, 2018. Early adoption is permitted as of the beginning of an annual reporting period for which financial statements, interim or annual, have not been issued. The amendments will be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. The Company is currently evaluating the impact that the adoption of this guidance will have on its consolidated financial statements and related disclosures.

In November 2016, the FASB issued ASU No. 2016-18 which requires entities to show the changes in the total of cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. As a result, the Company will no longer present transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. The guidance is effective for the Company's interim and annual reporting periods during the year ending December 31, 2018. Early adoption is permitted, including adoption in an interim period. The amendments will be applied using a retrospective transition method to each period presented. The Company will be required to apply the guidance retrospectively when adopted. The Company does not believe that the adoption of this accounting guidance will have a material impact on its consolidated financial statements and related disclosures.

In January 2017, the FASB issued ASU No. 2017-01 which provides guidance to assist entities with evaluating when a set of transferred assets and activities is a business. Under the updated guidance, a set is not a business if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or a group of similar assets. If the threshold is not met, the update requires that, to be a business, the set must include, at a minimum, an input and a substantive process that together significantly contribute to the ability to create outputs. The definition of outputs was also aligned with Accounting Standard Codification, or ASC, 606 by focusing on revenue-generating activities. The guidance is effective for the Company’s interim and annual reporting periods during the year ending December 31, 2018, and prospectively applicable to any transactions occurring within the period of adoption. Early adoption is permitted. The Company is currently evaluating the impact that the adoption of this guidance will have on its consolidated financial statements and related disclosures.

In January 2017, the FASB issued ASU No. 2017-04 which eliminates the requirement to calculate the implied fair value of goodwill. An entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The FASB also eliminated the requirements for any reporting unit with a zero or negative carrying amount to perform a qualitative assessment and, if it fails that qualitative test, to perform Step 2 of the goodwill impairment test. An entity is required to disclose the amount of goodwill allocated to each reporting unit with a zero or negative carrying amount of net assets. The guidance is effective for the Company’s interim and annual reporting periods during the year ending December 31, 2020, and applied on a prospective basis. Early adoption is permitted for interim and annual goodwill impairment testing dates after January 1, 2017. The Company is currently evaluating the impact that the adoption of this guidance will have on its consolidated financial statements and related disclosures.