Amphastar Pharmaceuticals (AMPH) 10-Q 7 May 21 2021 Q1 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2021	May 03, 2021
Document and Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-36509
Entity Registrant Name	Amphastar Pharmaceuticals, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	33-0702205
Entity Address, Address Line One	11570 6th Street
Entity Address, City or Town	Rancho Cucamonga
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	91730
City Area Code	909
Local Phone Number	980-9484
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	AMPH
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		47,635,351
Entity Central Index Key	0001297184
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current Assets:
Cash and cash equivalents	$ 101,601	$ 92,642
Restricted cash	235	1,865
Short-term investments	13,531	12,977
Restricted short-term investments	2,200	2,200
Accounts receivable, net	77,938	66,005
Inventories	97,110	96,831
Income tax refunds and deposits	800	385
Prepaid expenses and other assets	6,749	6,777
Total current assets	300,164	279,682
Property, plant, and equipment, net	253,265	260,055
Finance lease right-of-use assets	594	612
Operating lease right-of-use assets	19,280	20,042
Goodwill and intangible assets, net	40,243	40,615
Other assets	7,212	5,250
Deferred tax assets	24,980	24,980
Total assets	645,738	631,236
Current Liabilities:
Accounts payable and accrued liabilities	108,545	95,504
Income taxes payable	2,676	1,077
Current portion of long-term debt	12,173	12,263
Current portion of operating lease liabilities	3,702	3,357
Total current liabilities	127,096	112,201
Long-term reserve for income tax liabilities	4,709	4,709
Long-term debt, net of current portion	32,334	34,186
Long-term operating lease liabilities, net of current portion	16,464	17,464
Deferred tax liabilities	755	741
Other long-term liabilities	13,420	13,212
Total liabilities	194,778	182,513
Stockholders' equity:
Preferred stock: par value $0.0001; 20,000,000 shares authorized; no shares issued and outstanding
Common stock: par value $0.0001; 300,000,000 shares authorized; 55,184,000 and 47,718,003 shares issued and outstanding as of March 31, 2021 and 54,760,922 and 47,495,439 shares issued and outstanding as of December 31, 2020, respectively	6	5
Additional paid-in capital	413,926	410,061
Retained earnings	122,814	117,773
Accumulated other comprehensive loss	(5,642)	(3,721)
Treasury stock	(125,546)	(121,812)
Total Amphastar Pharmaceuticals, Inc. stockholders' equity	405,558	402,306
Non-controlling Interests	45,402	46,417
Total equity	450,960	448,723
Total liabilities and stockholders' equity	$ 645,738	$ 631,236

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
CONSOLIDATED BALANCE SHEETS
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock; shares authorized	300,000,000	300,000,000
Common stock; shares issued	55,184,000	54,760,922
Common stock; shares outstanding	47,718,003	47,495,439

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CONSOLIDATED STATEMENTS OF OPERATIONS
Net revenues	$ 103,020	$ 84,688
Cost of revenues	58,074	47,865
Gross profit	44,946	36,823
Operating (income) expenses:
Selling, distribution, and marketing	4,537	3,294
General and administrative	15,338	10,746
Research and development	14,765	15,303
Total operating expenses	34,640	29,343
Income (loss) from operations	10,306	7,480
Non-operating (expenses) income:
Interest income	161	153
Interest expense	(104)	(76)
Other income (expenses), net	(5,249)	(1,752)
Total non-operating (expenses) income, net	(5,192)	(1,675)
Income (loss) before income taxes	5,114	5,805
Income tax provision (benefit)	1,155	2,280
Net income (loss)	3,959	3,525
Net income (loss) attributable to non-controlling interests	(1,082)	(424)
Net income (loss) attributable to Amphastar Pharmaceuticals, Inc.	$ 5,041	$ 3,949
Net income (loss) per share attributable to Amphastar Pharmaceuticals, Inc. stockholders:
Basic (in Dollars per share)	$ 0.11	$ 0.09
Diluted (in Dollars per share)	$ 0.10	$ 0.08
Weighted-average shares used to compute net income (loss) per share attributable to Amphastar Pharmaceuticals, Inc. stockholders:
Basic (in Shares)	47,520	46,408
Diluted (in Shares)	49,518	48,248

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss) attributable to Amphastar Pharmaceuticals, Inc.	$ 5,041	$ 3,949
Other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc., net of income taxes
Foreign currency translation adjustment	(1,921)	(774)
Total other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.	(1,921)	(774)
Total comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.	$ 3,120	$ 3,175

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common stock	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Total Amphastar Stockholders' Equity [Member]	Non-controlling Interest [Member]	Total
Balance at Dec. 31, 2019	$ 5	$ 367,305	$ 116,370	$ (4,687)	$ (97,627)	$ 381,366	$ 46,162
Balance at Dec. 31, 2019								$ 427,528
Balance at Dec. 31, 2019	52,495,483				(5,918,515)
Changes in Stockholders' Equity
Net income (loss) attributable to Amphastar Pharmaceuticals, Inc.			3,949			3,949		3,949
Other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.				(774)		(774)		(774)
Net loss attributable to non-controlling interest							(424)	(424)
Treasury stock acquired					$ (10,950)	(10,950)		(10,950)
Treasury stock acquired (in Shares)					(647,246)
Issuance of treasury stock in connection with the Company's equity plans		(84)			$ 84
Issuance of treasury stock in connection with the Company's equity plans (in Shares)					6,873
Issuance of common stock in connection with the Company's equity plans		(1,238)				(1,238)		(1,238)
Issuance of common stock in connection with the Company's equity plans (in Shares)	369,508
Share-based compensation expense		5,161				5,161	121	5,282
Balance at Mar. 31, 2020	$ 5	371,144	120,319	(5,461)	$ (108,493)	377,514	45,859
Balance at Mar. 31, 2020								423,373
Balance at Mar. 31, 2020	52,864,991				(6,558,888)
Balance at Dec. 31, 2020	$ 5	410,061	117,773	(3,721)	$ (121,812)	402,306	46,417	402,306
Balance at Dec. 31, 2020								$ 448,723
Balance at Dec. 31, 2020	54,760,922				(7,265,483)			47,495,439
Changes in Stockholders' Equity
Net income (loss) attributable to Amphastar Pharmaceuticals, Inc.			5,041			5,041		$ 5,041
Other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.				(1,921)		(1,921)		(1,921)
Net loss attributable to non-controlling interest							(1,082)	(1,082)
Treasury stock acquired					$ (3,783)	(3,783)		(3,783)
Treasury stock acquired (in Shares)					(204,698)
Issuance of treasury stock in connection with the Company's equity plans		(49)			$ 49
Issuance of treasury stock in connection with the Company's equity plans (in Shares)					4,184
Issuance of common stock in connection with the Company's equity plans	$ 1	(853)				(852)		(852)
Issuance of common stock in connection with the Company's equity plans (in Shares)	423,078
Share-based compensation expense		4,767				4,767	67	4,834
Balance at Mar. 31, 2021	$ 6	$ 413,926	$ 122,814	$ (5,642)	$ (125,546)	$ 405,558	$ 45,402	405,558
Balance at Mar. 31, 2021								$ 450,960
Balance at Mar. 31, 2021	55,184,000				(7,465,997)			47,718,003

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash Flows From Operating Activities:
Net income (loss)	$ 3,959	$ 3,525
Reconciliation to net cash provided by operating activities:
Loss (gain) on impairment and disposal of assets	6	14
Depreciation of property, plant, and equipment	5,686	4,716
Amortization of product rights, trademarks, and patents	276	258
Operating lease right-of-use asset amortization	863	848
Share-based compensation	4,834	5,282
Changes in deferred taxes, net		1,638
Changes in operating assets and liabilities:
Accounts receivable, net	(12,078)	(12,487)
Inventories	(1,144)	2,241
Prepaid expenses and other assets	1,119	1,494
Income tax refunds, deposits, and payables, net	1,182	451
Operating lease liabilities	(754)	(824)
Accounts payable and accrued liabilities	18,876	(5,679)
Net cash provided by operating activities	22,825	1,477
Cash Flows From Investing Activities:
Purchases and construction of property, plant, and equipment	(7,618)	(8,006)
Sales of short-term investments, net		21
Purchase of short-term investments	(4,501)	(4,561)
Maturity of short-term investments	3,944	4,030
Payment of deposits and other assets	(520)	(206)
Net cash used in investing activities	(8,695)	(8,722)
Cash Flows From Financing Activities:
Proceeds from equity plans, net of withholding tax payments	(854)	(1,238)
Purchase of treasury stock	(3,783)	(10,950)
Proceeds from issuance of long-term debt		3,067
Principal payments on long-term debt	(2,002)	(2,328)
Net cash provided by (used in) financing activities	(6,639)	(11,449)
Effect of exchange rate changes on cash	(162)	(146)
Net increase (decrease) in cash, cash equivalents and restricted cash	7,329	(18,840)
Cash, cash equivalents, and restricted cash at beginning of period	94,507	75,550
Cash, cash equivalents, and restricted cash at end of period	101,836	56,710
Noncash Investing and Financing Activities:
Capital expenditure included in accounts payable	6,238	5,840
Operating lease right-of-use assets	103
Equipment acquired under finance leases	74
Supplemental Disclosures of Cash Flow Information:
Interest paid, net of capitalized interest	508	559
Income taxes paid	$ 30	$ 209

General

General	3 Months Ended
	Mar. 31, 2021
General
General	Note 1. Genera l ​ Amphastar Pharmaceuticals, Inc., a Delaware corporation (together with its subsidiaries, hereinafter referred to as the “Company”) is a bio-pharmaceutical company that develops, manufactures, markets, and sells generic and proprietary injectable, inhalation, and intranasal products, including products with high technical barriers to market entry. Additionally, the Company sells insulin active pharmaceutical ingredient, or API, products. Most of the Company’s products are used in hospital or urgent care clinical settings and are primarily contracted and distributed through group purchasing organizations and drug wholesalers. The Company’s insulin API products are sold to other pharmaceutical companies for use in their own products and are being used by the Company in the development of injectable finished pharmaceutical products. The Company’s inhalation product, Primatene Mist ® ​ The accompanying unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements of the Company for the year ended December 31, 2020 and the notes thereto as filed with the Securities and Exchange Commission, or SEC, in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with generally accepted accounting principles, or GAAP, have been condensed or omitted from the accompanying condensed consolidated financial statements. The accompanying year-end condensed consolidated balance sheet was derived from the audited financial statements. The accompanying interim financial statements are unaudited, but reflect all adjustments which are, in the opinion of management, necessary for a fair statement of the Company’s consolidated financial position, results of operations, comprehensive income (loss), stockholders’ equity, and cash flows for the periods presented. Unless otherwise noted, all such adjustments are of a normal, recurring nature. The Company’s results of operations, comprehensive income (loss) and cash flows for the interim periods are not necessarily indicative of the results of operations and cash flows that it may achieve in future periods.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	Note 2. Summary of Significant Accounting Policies ​ Basis of Presentation ​ The unaudited condensed consolidated financial statements include the accounts of the Company and its subsidiaries, and are prepared in accordance with United States generally accepted accounting principles, or GAAP. Certain prior period amounts have been reclassified within the investing activities of the statement of cash flows to conform to the current period presentation. All intercompany activity has been eliminated in the preparation of the condensed consolidated financial statements. ​ 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 Biological Technology Co., Ltd., or Letop, (5) Nanjing Hanxin Pharmaceutical Technology Co., Ltd., or Hanxin, (6) Nanjing Hanxin Biomedical Testing Service Co., Ltd., or Hanxin Biomedical, (7) Nanjing Baixin Trading Co., Ltd., or Baixin, (8) Amphastar France Pharmaceuticals, S.A.S., or AFP, (9) Amphastar UK Ltd., or AUK, and (10) International Medication Systems (UK) Limited, or IMS UK. ​ In July 2018, the Company’s Chinese subsidiary, ANP, completed a private placement of its common equity interest to accredited investors and received approximately $56.3 million of cash proceeds, a portion of which was received in 2019. The Company has retained approximately 58% of the equity interest in ANP following the private placement and continues to consolidate the financial results of ANP with the Company’s results of operations. ANP’s net income after July 2, 2018, was attributed to the Company in accordance with the Company’s equity interest of approximately 58% in ANP. COVID-19 Pandemic ​ The Company is subject to risks and uncertainties as a result of the ongoing novel coronavirus pandemic, or COVID-19. The complete extent of the impact of the COVID-19 pandemic on the Company’s business is highly uncertain and difficult to predict, as the information is constantly evolving. The Company considered the impact of COVID - ​ All of the Company’s production facilities continued to operate during the quarter as they had prior to the COVID-19 pandemic with very little change, other than for enhanced safety measures intended to prevent the spread of the virus. ​ It is not possible at this time to estimate the complete impact that COVID-19 could have on the Company’s business, including its customers and suppliers, as the impact will depend on future developments, which are highly uncertain and cannot be predicted. The Company will continue to monitor the impact of COVID-19 on all aspects of its business. ​ Use of Estimates ​ The preparation of condensed consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Actual results could differ from those estimates. The principal accounting estimates include: determination of allowances for credit losses, allowance for discounts, provision for chargebacks and rebates, provision for product returns, adjustment of inventory to their net realizable values, impairment of long-lived and intangible assets and goodwill, 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 US Dollar. ANP maintains its books of record in Chinese yuan. These books are remeasured into the functional currency of USD using 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 condensed consolidated statements of operations. ​ The Company’s French subsidiary, AFP, maintains its book of record in euros. ANP’s subsidiaries maintain their books of record in Chinese yuan. AUK’s subsidiary, IMS UK, maintains its book of record in British pounds. These local currencies have been determined to be the subsidiaries’ respective functional currencies. These books of record 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, 2021 and 2020 were $1.5 million loss and $0.6 million loss, respectively. ​ Comprehensive Income (Loss) ​ For the three months ended March 31, 2021 and 2020, the Company included its foreign currency translation gain or loss as part of its comprehensive income (loss). No income tax expense (benefit) was allocated to other comprehensive income (loss) for the three months ended March 31, 2021 and 2020. ​ Advertising Expense ​ Advertising expenses, primarily associated with Primatene Mist ® ​ Financial Instruments ​ The carrying amounts of cash and cash equivalents, short-term investments, restricted cash and short-term investments, accounts receivable, accounts payable, accrued expenses, and short-term borrowings approximate fair value due to the short maturity of these items. The 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. 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. ​ Cash and Cash Equivalents ​ Cash and cash equivalents consist of cash, money market accounts, certificates of deposit and highly liquid investments purchased with original maturities of three months or less. ​ Short-Term Investments ​ Short-term investments as of March 31, 2021 and December 31, 2020 consisted of certificates of deposit and investment grade debt securities with original expiration dates within 12 months. ​ Restricted Cash ​ Restricted cash is collateral required for the Company to guarantee certain vendor payments in France. As of March 31, 2021 and December 31, 2020, the restricted cash balance was $0.2 million and $1.9 million, respectively. ​ Restricted Short-Term Investments ​ Restricted short-term investments consist of certificates of deposit that are collateral for standby letters of credit to qualify for workers’ compensation self-insurance. The certificates of deposit have original maturities greater than three months, but less than one year. As of March 31, 2021 and December 31, 2020, the balance of restricted short-term investments was $2.2 million. ​ 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. ​ Recent Accounting Pronouncements ​ In December 2019, the Financial Accounting Standards Board, or FASB, issued Accounting Standard Update, or ASU, No. 2019-12 Simplifying the Accounting for Income Taxes (Topic 740)

Revenue Recognition

Revenue Recognition	3 Months Ended
	Mar. 31, 2021
Revenue Recognition
Revenue Recognition	Note 3. Revenue Recognition ​ In accordance with Accounting Standard Codification, or ASC, 606 Revenue from Contracts with Customers ​ Generally, revenue is recognized at the time of product delivery to the Company’s customers. In some cases, revenue is recognized at the time of shipment when stipulated by the terms of the sale agreements. ​ The consideration the Company receives in exchange for its goods or services is only recognized when it is probable that a significant reversal will not occur. The consideration to which the Company expects to be entitled includes a stated list price, less various forms of variable consideration. The Company makes significant estimates for related variable consideration at the point of sale, including chargebacks, rebates, product returns, other discounts and allowances. ​ The Company’s payment terms vary by types and locations of customers and the products or services offered. Payment terms differ by jurisdiction and customers, but payment is generally required in a term ranging from 30 to 75 days from date of shipment or satisfaction of the performance obligation. For certain products or services and certain customer types, we may require payment before products are delivered or services are rendered to customers. ​ Provisions for estimated chargebacks, rebates, discounts, product returns and credit losses are made at the time of sale and are analyzed and adjusted, if necessary, at each balance sheet date. ​ Revenues derived from contract manufacturing services are recognized when third-party products are shipped to customers, and after the customer has accepted test samples of the products to be shipped. ​ The Company’s accounting policy is to review each agreement involving contract development and manufacturing services to determine if there are multiple revenue-generating activities that constitute more than one unit of accounting. Revenues are recognized for each unit of accounting based on revenue recognition criteria relevant to that unit. The Company does not have any revenue arrangements with multiple performance obligations. ​ Provision for Chargebacks and Rebates ​ The provision for chargebacks and rebates is a significant estimate used in the recognition of revenue. Wholesaler chargebacks relate to sales terms under which the Company agrees to reimburse wholesalers for differences between the gross sales prices at which the Company sells its products to wholesalers and the actual prices of such products that wholesalers resell under the Company’s various contractual arrangements with third parties such as hospitals and group purchasing organizations in the United States. Rebates include primarily amounts paid to retailers, payers, and providers in the United States, including those paid to state Medicaid programs, and are based on contractual arrangements or statutory requirements. The Company estimates chargebacks and rebates using the expected value method at the time of sale to wholesalers based on wholesaler inventory stocking levels, historic chargeback and rebate rates, and current contract pricing. ​ The provision for chargebacks and rebates is reflected as a component of net revenues. The following table is an analysis of the chargeback and rebate provision: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 20,380 $ 21,644 ​ Provision for chargebacks and rebates ​ 47,031 ​ 35,987 ​ Credits and payments issued to third parties ​ (46,881) ​ (39,353) ​ Ending balance ​ $ 20,530 ​ $ 18,278 ​ ​ Changes in the chargeback provision from period to period are primarily dependent on the Company’s sales to its wholesalers, the level of inventory held by wholesalers, and the wholesalers’ customer mix. Changes in the rebate provision from period to period are primarily dependent on retailer’s and other indirect customers’ purchases. The approach that the Company uses to estimate chargebacks has been consistently applied for all periods presented. Variations in estimates have been historically small. The Company continually monitors the provision for chargebacks and rebates and makes adjustments when it believes that the actual chargebacks and rebates may differ from the estimates. The settlement of chargebacks and rebates generally occurs within 30 days to 60 days after the sale to wholesalers. Accounts receivable and/or accounts payable and accrued liabilities are reduced and/or increased by the chargebacks and rebate amounts depending on whether the Company has the right to offset with the customer. Of the provision for chargebacks and rebates as of March 31, 2021 and December 31, 2020, $16.4 million and $16.4 million were included in accounts receivable, net, on the condensed consolidated balance sheets, respectively. The remaining provision as of March 31, 2021 and December 31, 2020 of $4.1 million and $4.0 million, respectively, were included in accounts payable and accrued liabilities. ​ Accrual for Product Returns ​ The Company offers most customers the right to return qualified excess or expired inventory for partial credit; however, API product sales are generally non-returnable. The Company’s product returns primarily consist of the returns of expired products from sales made in prior periods. Returned products cannot be resold. At the time product revenue is recognized, the Company records an accrual for product returns estimated using the expected value method. The accrual is based, in part, upon the historical relationship of product returns to sales and customer contract terms. The Company also assesses other factors that could affect product returns including market conditions, product obsolescence, and the introduction of new competition. Although these factors do not normally give the Company’s customers the right to return products outside of the regular return policy, the Company realizes that such factors could ultimately lead to increased returns. The Company analyzes these situations on a case-by-case basis and makes adjustments to the product return reserve as appropriate. ​ The provision for product returns is reflected as a component of net revenues. The following table is an analysis of the product return liability: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 14,204 $ 10,339 ​ Provision for product returns ​ 3,233 ​ 3,099 ​ Credits issued to third parties ​ (2,517) ​ (2,239) ​ Ending balance ​ $ 14,920 ​ $ 11,199 ​ ​ Of the provision for product returns as of March 31, 2021 and December 31, 2020, $10.7 million and $10.2 million, were included in accounts payable and accrued liabilities on the condensed consolidated balance sheets, respectively. The remaining provision as of March 31, 2021 and December 31, 2020 of $4.2 million and $4.0 million, respectively, were included in other long-term liabilities. For the three months ended March 31, 2021 and 2020, the Company’s aggregate product return rate was 1.4% and 1.1% of qualified sales, respectively.

Income (Loss) per Share Attribu

Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders	3 Months Ended
	Mar. 31, 2021
Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders
Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders	Note 4. Income per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders ​ Basic net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders is calculated based upon the weighted-average number of shares outstanding during the period. Diluted net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders gives effect to all potential dilutive shares outstanding during the period, such as stock options, non-vested restricted stock units and shares issuable under the Company’s Employee Stock Purchase Plan, or ESPP and the reallocation of net income attributable to non-controlling interest from the assumed dilutive effect of stock options issued under the 2018 ANP Equity Incentive Plan, or the 2018 Plan. ​ For the three months ended March 31, 2021, options to purchase 1,899,833 shares of stock with a weighted-average exercise price of $20.85 per share, and the reallocation of net income attributable to non-controlling interests were excluded in the computation of diluted net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders because the effect would be anti-dilutive. ​ For the three months ended March 31, 2020, options to purchase 1,999,083 shares of stock with a weighted-average exercise price of $20.81 per share, and the reallocation of net income attributable to non-controlling interest were excluded in the computation of diluted net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders because the effect would be anti-dilutive. ​ The following table provides the calculation of basic and diluted net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders for each of the periods presented: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ ​ (in thousands, except per share data) ​ Basic and dilutive numerator: ​ ​ Net income attributable to Amphastar Pharmaceuticals, Inc. ​ $ 5,041 ​ $ 3,949 ​ Denominator: ​ ​ ​ ​ ​ ​ ​ Weighted-average shares outstanding — basic ​ 47,520 ​ 46,408 ​ ​ ​ ​ ​ ​ ​ ​ ​ Net effect of dilutive securities: ​ ​ ​ ​ ​ ​ ​ Incremental shares from equity awards ​ 1,998 ​ 1,840 ​ Weighted-average shares outstanding — diluted ​ 49,518 ​ 48,248 ​ Net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders — basic ​ $ 0.11 ​ $ 0.09 ​ Net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders — diluted ​ $ 0.10 ​ $ 0.08 ​ ​

Segment Reporting

Segment Reporting	3 Months Ended
	Mar. 31, 2021
Segment Reporting
Segment Reporting	Note 5. Segment Reporting ​ The Company’s business is the development, manufacture, and marketing of pharmaceutical products. The Company has identified two reporting segments that each report to the Chief Operating Decision Maker, or CODM, as defined in ASC 280, Segment Reporting. The Company’s performance is assessed and resources are allocated by the CODM based on the following two reportable segments: ​ ● Finished pharmaceutical products ● API ​ The finished pharmaceutical products segment manufactures, markets and distributes Primatene Mist ® ​ Selected financial information by reporting segment is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Net revenues: ​ ​ Finished pharmaceutical products ​ $ 97,882 ​ $ 81,298 ​ API ​ 5,138 ​ ​ 3,390 ​ Total net revenues ​ 103,020 ​ 84,688 ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross profit (loss): ​ ​ ​ ​ ​ ​ ​ Finished pharmaceutical products ​ 45,286 ​ 38,810 ​ API ​ (340) ​ ​ (1,987) ​ Total gross profit ​ 44,946 ​ 36,823 ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating expenses ​ 34,640 ​ 29,343 ​ ​ ​ ​ ​ ​ ​ ​ ​ Income from operations ​ 10,306 ​ 7,480 ​ Non-operating expense ​ (5,192) ​ (1,675) ​ ​ ​ ​ ​ ​ ​ ​ ​ Income before income taxes ​ $ 5,114 ​ $ 5,805 ​ ​ The Company manages its business segments to the gross profit level and manages its operating and other costs on a company-wide basis. The Company does not identify total assets by segment for internal purposes, as the Company’s CODM does not assess performance, make strategic decisions, or allocate resources based on assets. ​ ​ The amount of net revenues in the finished pharmaceutical product segment is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Finished pharmaceutical products net revenues: ​ ​ Primatene Mist ® ​ $ 18,383 ​ $ 12,877 ​ Epinephrine ​ ​ 15,578 ​ ​ 3,990 ​ Enoxaparin ​ ​ 10,658 ​ ​ 9,168 ​ Phytonadione ​ 9,565 ​ 11,029 ​ Lidocaine ​ ​ 9,071 ​ ​ 10,657 ​ Glucagon ​ ​ 7,984 ​ ​ — ​ Naloxone ​ ​ 6,341 ​ ​ 8,875 ​ Other finished pharmaceutical products ​ 20,302 ​ 24,702 ​ Total finished pharmaceutical products net revenues ​ $ 97,882 ​ $ 81,298 ​ ​ The amount of depreciation and amortization expense included in cost of revenues, by reporting segments is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Depreciation and amortization expense ​ ​ Finished pharmaceutical products ​ $ 1,435 ​ $ 1,464 ​ API ​ 1,048 ​ 582 ​ Total depreciation and amortization expense ​ $ 2,483 ​ $ 2,046 ​ ​ Net revenues and carrying values of long-lived assets by geographic regions are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net Revenue ​ Long-Lived Assets ​ ​ Three Months Ended ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ March 31, ​ December 31, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ (in thousands) United States $ 99,170 $ 81,065 $ 125,861 $ 129,401 ​ China ​ 1,121 ​ ​ 228 ​ 97,847 ​ 98,538 ​ France ​ 2,729 ​ ​ 3,395 ​ 49,431 ​ 52,770 ​ Total ​ $ 103,020 ​ $ 84,688 ​ $ 273,139 ​ $ 280,709 ​ ​

Customer and Supplier Concentra

Customer and Supplier Concentration	3 Months Ended
	Mar. 31, 2021
Customer and Supplier Concentration
Customer and Supplier Concentration	Note 6. Customer and Supplier Concentration ​ Customer Concentrations ​ Three large wholesale drug distributors, AmerisourceBergen Corporation, or AmerisourceBergen, Cardinal Health, Inc., or Cardinal, and McKesson Corporation, or McKesson, are all distributors of the Company’s products, as well as suppliers of a broad range of health care products. The Company considers these three customers to be its major customers, as each individually, and these customers collectively, represented a significant percentage of the Company’s net revenue for the three months ended March 31, 2021 and 2020 and accounts receivable as of March 31, 2021 and December 31, 2020, respectively. The following table provides accounts receivable and net revenue information for these major customers: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ % of Total Accounts ​ % of Net ​ ​ ​ Receivable ​ Revenue ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ December 31, ​ March 31, ​ ​ 2021 2020 2021 2020 AmerisourceBergen 14 % 9 % 25 % 24 % McKesson 21 % 24 % 20 % 22 % Cardinal Health 16 % 17 % 15 % 19 % ​ Supplier Concentrations ​ The Company depends on suppliers for raw materials, APIs, and other components that are subject to stringent FDA requirements. Some of these materials may only be available from one or a limited number of sources. Establishing additional or replacement suppliers for these materials may take a substantial period of time, as suppliers must be approved by the FDA. Furthermore, a significant portion of raw materials may only be available from foreign sources. If the Company is unable to secure, on a timely basis, sufficient quantities of the materials it depends on to manufacture and market its products, it could have a materially adverse effect on the Company’s business, financial condition, and results of operations.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Measurements
Fair Value Measurements	Note 7. Fair Value Measurements ​ GAAP defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants in the principal or most advantageous market for the asset or liability at the measurement date (an exit price). These standards also establish a hierarchy that prioritizes observable and unobservable inputs used in measuring fair value of an asset or liability, as described below: ​ ● Level 1 – Inputs to measure fair value are based on quoted prices (unadjusted) in active markets on identical assets or liabilities; ​ ● Level 2 – Inputs to measure fair value are based on the following: a) quoted prices in active markets on similar assets or liabilities, b) quoted prices for identical or similar instruments in inactive markets, or c) observable (other than quoted prices) or collaborated observable market data used in a pricing model from which the fair value is derived; and ​ ● Level 3 – Inputs to measure fair value are unobservable and the assets or liabilities have little, if any, market activity; these inputs reflect the Company’s own assumptions about the assumptions that market participants would use in pricing the assets or liabilities based on best information available in the circumstances. ​ As of March 31, 2021, cash equivalents include money market accounts. Short-term investments consist of certificates of deposit as well as investment-grade corporate and municipal bonds with original expiration dates within 12 months. The certificates of deposit are carried at amortized cost in the Company’s condensed consolidated balance sheet, which approximates their fair value determined based on Level 2 inputs. The corporate and municipal bonds are classified as held-to-maturity and are carried at amortized cost net of allowance for credit losses, which approximates their fair value determined based on Level 2 inputs. The restrictions on restricted cash and short-term investments have a negligible effect on the fair value of these financial assets. ​ ​ The fair value of the Company’s financial assets and liabilities measured on a recurring basis as of March 31, 2021 and December 31, 2020, are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total (Level 1) (Level 2) (Level 3) ​ ​ (in thousands) Cash equivalents - money market ​ $ 76,536 ​ $ 76,536 ​ $ — ​ $ — ​ Restricted cash - money market ​ ​ 235 ​ ​ 235 ​ ​ — ​ ​ — ​ Short-term investments - certificates of deposit ​ ​ 9,284 ​ ​ — ​ ​ 9,284 ​ ​ — ​ Restricted short-term investments - certificates of deposit ​ 2,200 ​ — ​ 2,200 ​ — ​ Corporate and municipal bonds ​ ​ 4,199 ​ ​ — ​ ​ 4,199 ​ ​ — ​ Interest rate swap liabilities related to variable rate loans ​ ​ (723) ​ ​ — ​ ​ (723) ​ ​ — ​ Fair value measurement as of March 31, 2021 ​ $ 91,731 ​ $ 76,771 ​ $ 14,960 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents - money market ​ $ 58,710 ​ $ 58,710 ​ $ — ​ $ — ​ Restricted cash - money market ​ ​ 1,865 ​ ​ 1,865 ​ ​ — ​ ​ — ​ Short-term investments - certificates of deposit ​ ​ 9,089 ​ ​ — ​ ​ 9,089 ​ ​ — ​ Restricted short-term investments - certificates of deposit ​ 2,200 ​ — ​ 2,200 ​ — ​ Corporate and municipal bonds ​ ​ 3,855 ​ ​ — ​ ​ 3,855 ​ ​ — ​ Interest rate swap liabilities related to variable rate loans ​ ​ (902) ​ ​ — ​ ​ (902) ​ ​ — ​ Fair value measurement as of December 31, 2020 ​ $ 74,817 ​ $ 60,575 ​ $ 14,242 ​ $ — ​ ​ The Company does not hold any Level 3 instruments that are measured at fair value on a recurring basis. ​ Nonfinancial assets and liabilities are not measured at fair value on a recurring basis but are subject to fair value adjustments in certain circumstances. These items primarily include long-lived assets, goodwill, and intangible assets for which the fair value of assets is determined as part of the related impairment test. As of March 31, 2021 and December 31, 2020, there were no significant adjustments to fair value for nonfinancial assets or liabilities.

Investments

Investments	3 Months Ended
	Mar. 31, 2021
Investments
Investments	Note 8. Investments ​ A summary of the Company’s investments that are classified as held-to-maturity are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) Corporate bonds ​ $ 1,053 ​ $ — ​ $ (1) ​ $ 1,052 Municipal bonds ​ ​ 3,148 ​ ​ — ​ ​ (1) ​ ​ 3,147 Total investments as of March 31, 2021 ​ $ 4,201 ​ $ — ​ $ (2) ​ $ 4,199 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate bonds ​ $ 1,560 ​ $ — ​ $ (1) ​ $ 1,559 Municipal bonds ​ ​ 2,297 ​ ​ — ​ ​ (1) ​ ​ 2,296 Total investments as of December 31, 2020 ​ $ 3,857 ​ $ — ​ $ (2) ​ $ 3,855 ​ At each reporting period, the Company evaluates securities for impairment when the fair value of the investment is less than its amortized cost. The Company evaluated the underlying credit quality and credit ratings of the issuers, noting neither a significant deterioration since purchase nor any other factors that would indicate a material credit loss. ​ The Company measures expected credit losses on held-to-maturity investments on a collective basis. All the Company’s held-to-maturity investments were considered to be one pool. The estimate for credit losses considers historical loss information that is adjusted for current conditions and reasonable and supportable forecasts. Expected credit losses on held-to-maturity investments were not material to the condensed consolidated financial statements .

Goodwill and Intangible Assets

Goodwill and Intangible Assets	3 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets
Goodwill and Intangible Assets	Note 9. Goodwill and Intangible Assets ​ The table below shows the weighted-average life, original cost, accumulated amortization, and net book value by major intangible asset classification: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Accumulated ​ ​ ​ ​ Life (Years) Original Cost Amortization Net Book Value ​ ​ (in thousands) Definite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ IMS (UK) international product rights ​ 10 ​ $ 9,640 ​ $ 4,499 ​ $ 5,141 ​ Patents 12 ​ 486 ​ ​ 308 ​ 178 ​ Land-use rights 39 ​ 2,540 ​ ​ 634 ​ 1,906 ​ Subtotal 12 ​ 12,666 ​ 5,441 ​ 7,225 ​ Indefinite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Trademark * ​ 29,225 ​ — ​ 29,225 ​ Goodwill - Finished pharmaceutical products * ​ 3,793 ​ — ​ 3,793 ​ Subtotal * ​ 33,018 ​ — ​ 33,018 ​ As of March 31, 2021 * ​ $ 45,684 ​ $ 5,441 ​ $ 40,243 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Accumulated ​ ​ ​ ​ Life (Years) Original Cost Amortization Net Book Value ​ ​ (in thousands) Definite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ IMS (UK) international product rights ​ 10 ​ $ 9,561 ​ $ 4,223 ​ $ 5,338 ​ Patents 12 ​ 486 ​ ​ 297 ​ 189 ​ Land-use rights 39 ​ 2,540 ​ ​ 617 ​ 1,923 ​ Subtotal 12 ​ 12,587 ​ 5,137 ​ 7,450 ​ Indefinite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Trademark * ​ 29,225 ​ — ​ 29,225 ​ Goodwill - Finished pharmaceutical products * ​ 3,940 ​ — ​ 3,940 ​ Subtotal * ​ 33,165 ​ — ​ 33,165 ​ As of December 31, 2020 * ​ $ 45,752 ​ $ 5,137 ​ $ 40,615 ​ * Intangible assets with indefinite lives have an indeterminable average life. ​ Goodwill ​ The changes in the carrying amounts of goodwill were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 3,940 $ 3,634 ​ Currency translation ​ (147) ​ 306 ​ Ending balance ​ $ 3,793 ​ $ 3,940 ​ ​ Primatene ® Trademark ​ In January 2009, the Company acquired the exclusive rights to the trademark, domain name, website and domestic marketing, distribution and selling rights related to Primatene Mist ® ​ The trademark was determined to have an indefinite life. In determining its indefinite life, the Company considered the following: the expected use of the intangible; the longevity of the brand; the legal, regulatory and contractual provisions that affect their maximum useful life; the Company’s ability to renew or extend the asset’s legal or contractual life without substantial costs; effects of the regulatory environment; expected changes in distribution channels; maintenance expenditures required to obtain the expected future cash flows from the asset; and considerations for obsolescence, demand, competition and other economic factors.

Inventories

Inventories	3 Months Ended
	Mar. 31, 2021
Inventories
Inventories	Note 10. Inventories ​ Inventories consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Raw materials and supplies $ 43,258 $ 47,051 ​ Work in process ​ 35,081 ​ 37,257 ​ Finished goods ​ 18,771 ​ 12,523 ​ Total inventories ​ $ 97,110 ​ $ 96,831 ​ ​ Charges of $9.5 million and $2.1 million were included in the cost of revenues in the Company’s condensed consolidated statements of operations for the three months ended March 31, 2021 and 2020, respectively, to adjust the Company’s inventory and related firm purchase commitments to their net realizable value. ​ Losses on firm purchase commitments related to raw materials on order were $8.6 million and $2.1 million as of March 31, 2021 and 2020, respectively.

Property, Plant, and Equipment

Property, Plant, and Equipment	3 Months Ended
	Mar. 31, 2021
Property, Plant, and Equipment
Property, Plant, and Equipment	Note 11. Property, Plant, and Equipment ​ Property, plant, and equipment consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Buildings $ 124,952 $ 124,326 ​ Leasehold improvements ​ 30,093 ​ 30,028 ​ Land ​ 7,659 ​ 7,719 ​ Machinery and equipment ​ 210,776 ​ 211,666 ​ Furniture, fixtures, and automobiles ​ 26,862 ​ 26,482 ​ Construction in progress ​ 42,165 ​ 43,981 ​ Total property, plant, and equipment ​ 442,507 ​ 444,202 ​ Less accumulated depreciation ​ (189,242) ​ (184,147) ​ Total property, plant, and equipment, net ​ $ 253,265 ​ $ 260,055 ​ ​

Accounts Payable and Accrued Li

Accounts Payable and Accrued Liabilities	3 Months Ended
	Mar. 31, 2021
Accounts Payable and Accrued Liabilities.
Accounts Payable and Accrued Liabilities	Note 12. Accounts Payable and Accrued Liabilities ​ Accounts payable and accrued liabilities consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ 2021 ​ 2020 ​ (in thousands) Accrued customer fees and rebates $ 10,466 ​ $ 9,029 Accrued payroll and related benefits ​ 26,742 ​ ​ 24,597 Accrued product returns, current portion ​ 10,676 ​ ​ 10,190 Accrued loss on firm purchase commitments ​ 8,625 ​ ​ 1,223 Accrued litigation and settlements ​ 19,449 ​ ​ 13,780 Other accrued liabilities ​ 9,600 ​ ​ 12,328 Total accrued liabilities 85,558 ​ 71,147 Accounts payable 22,987 ​ 24,357 Total accounts payable and accrued liabilities $ 108,545 ​ $ 95,504 ​

Debt

Debt	3 Months Ended
	Mar. 31, 2021
Debt
Debt	Note 13. Debt ​ Debt consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Line of Credit Facilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Line of credit facility with China Everbright Bank due June 2021 ​ $ 763 ​ $ 764 ​ Line of credit facility with China Merchant Bank due August 2021 ​ ​ 381 ​ ​ 382 ​ Line of credit facility with Bank of Nanjing due October 2021 ​ ​ 153 ​ ​ 153 ​ Line of credit facility with Cathay Bank due May 2022 ​ — ​ — ​ Line of credit facility with East West Bank due December 2022 ​ ​ — ​ ​ — ​ Equipment line of credit facility with East West Bank due September 2025 ​ ​ 3,216 ​ ​ 3,216 ​ ​ ​ ​ ​ ​ ​ ​ ​ Mortgage Loans ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mortgage payable with East West Bank due May 2021 ​ ​ 3,282 ​ ​ 3,306 ​ Mortgage payable with East West Bank due October 2026 ​ ​ 3,317 ​ ​ 3,334 ​ Mortgage payable with East West Bank due June 2027 ​ ​ 8,472 ​ ​ 8,510 ​ Mortgage payable with Cathay Bank due August 2027 ​ 7,220 ​ 7,268 ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment Loans ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment loan with East West Bank due June 2021 ​ ​ 306 ​ ​ 612 ​ Equipment loan with East West Bank due December 2022 ​ ​ 3,500 ​ ​ 4,000 ​ Equipment loan with East West Bank due February 2024 ​ ​ 4,839 ​ ​ 5,254 ​ ​ ​ ​ ​ ​ ​ ​ ​ Other Loans and Payment Obligations ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Acquisition loan with Cathay Bank due June 2024 ​ 8,137 ​ 8,710 ​ French government loan due July 2021 ​ ​ 64 ​ ​ 64 ​ French government loans due December 2026 ​ ​ 338 ​ ​ 350 ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment under Finance Leases ​ 519 ​ 526 ​ Total debt ​ 44,507 ​ 46,449 ​ Less current portion of long-term debt ​ 12,173 ​ 12,263 ​ Long-term debt, net of current portion ​ $ 32,334 ​ $ 34,186 ​ ​ As of March 31, 2021, the fair value of the loans listed above approximated their carrying amount. The interest rate used in the fair value estimation was determined to be a Level 2 input. For certain loans with East West Bank, the Company has entered into fixed interest rate swap contracts to exchange the variable interest rates for fixed interest rates over the life of certain debt instruments without the exchange of the underlying notional debt amount. ​ Covenants ​ At March 31, 2021 and December 31, 2020, the Company was in compliance with its debt covenants.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Taxes
Income Taxes	Note 14. Income Taxes ​ The following table sets forth the Company’s income tax provision for the periods indicated: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ 2021 2020 ​ ​ (in thousands) ​ Income before taxes ​ $ 5,114 ​ $ 5,805 ​ Income tax provision ​ ​ 1,155 ​ 2,280 ​ Net income ​ $ 3,959 ​ $ 3,525 ​ Income tax provision as a percentage of income before income taxes ​ ​ 22.6 % 39.3 % ​ The Company’s effective tax rate for the three months ended March 31, 2021 decreased in comparison to the three months ended March 31, 2020, primarily due to differences in pre-tax income positions and timing of discrete tax items. ​ Valuation Allowance ​ In assessing the need for a valuation allowance, management considers whether it is more likely than not that some portion or all of the deferred income tax assets will be realized. Ultimately, realization depends on the existence of future taxable income. Management considers sources of taxable income such as income in prior carryback periods, future reversal of existing deferred taxable temporary differences, tax-planning strategies, and projected future taxable income. ​ The Company continues to record a full valuation allowance on the net deferred income tax assets of its subsidiaries AFP and Hanxin and will continue to do so until the subsidiaries generate sufficient taxable income to realize their respective deferred income tax assets. ​ For purposes of computing its annual effective tax rate, the Company did not benefit from its losses in the states where it files separately. This increased the Company’s income tax expense by $0.1 million and $0.2 million during the three months ended March 31, 2021 and 2020, respectively.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2021
Stockholders' Equity
Stockholders' Equity	Note 15. Stockholders' Equity ​ Share Buyback Program ​ Pursuant to the Company’s existing share buyback program, the Company purchased 204,698 and 646,715 shares of its common stock during the three months ended March 31, 2021 and 2020, totaling $3.8 million and $10.9 million, respectively. ​ In August 2020, the Company’s Board of Directors authorized an increase of $20.0 million to the Company’s share buyback program, which is expected to continue for an indefinite period of time. The primary goal of the program is to offset dilution created by the Company’s equity compensation programs. ​ Purchases are made through open market and private block transactions pursuant to Rule 10b5-1 plans, privately negotiated transactions or other means as determined by the Company’s management and in accordance with the requirements of the SEC and applicable laws. The timing and actual number of treasury share purchases will depend on a variety of factors including price, corporate and regulatory requirements, and other conditions. These treasury share purchases are accounted for under the cost method and are included as a component of treasury stock in the Company’s condensed consolidated balance sheets. ​ Amended and Restated 2015 Equity Incentive Plan ​ As of March 31, 2021, the Company reserved an aggregate of 6,181,926 shares of common stock for future issuance under the Amended and Restated 2015 Equity Incentive Plan, or the 2015 Plan, including 1,187,386 shares, which were reserved in January 2021 pursuant to the evergreen provision in the 2015 Plan. ​ 2014 Employee Stock Purchase Plan ​ As of March 31, 2021, the Company has issued 807,550 shares of common stock under the ESPP and 1,192,450 shares of its common stock remains available for issuance under the ESPP. ​ For the three months ended March 31, 2021 and 2020, the Company recorded ESPP expense of $0.1 million and $0.1 million, respectively. ​ Share-Based Award Activity and Balances (excluding the ANP Equity Plan) ​ The Company accounts for share-based compensation payments in accordance with ASC 718, which requires measurement and recognition of compensation expense at fair value for all share-based payment awards made to employees and directors. Under these standards, the fair value of option awards and the option components of the Employee Stock Purchase Plan awards are estimated at the grant date using the Black-Scholes option-pricing model. The fair value of RSUs is estimated at the grant date using the Company’s common share price. The portion that is ultimately expected to vest is amortized and recognized in compensation expense on a straight-line basis over the requisite service period, generally from the grant date to the vesting date. ​ The weighted-averages for key assumptions used in determining the fair value of options granted during the three months ended March 31, 2021 and 2020, are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ ​ March 31, ​ ​ ​ 2021 2020 ​ Average volatility 42.2 % 43.0 % ​ Average risk-free interest rate 1.3 % 0.8 % ​ Weighted-average expected life in years 6.3 ​ 5.8 ​ ​ Dividend yield rate — % — % ​ ​ A summary of option activity for the three months ended March 31, 2021, is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ Remaining ​ Aggregate ​ ​ ​ ​ Exercise ​ Contractual ​ Intrinsic ​ ​ Options ​ Price ​ Term (Years) ​ Value (1) ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) Outstanding as of December 31, 2020 8,580,475 $ 15.00 ​ ​ Options granted 1,166,702 ​ 17.99 ​ ​ ​ ​ ​ ​ Options exercised (173,436) ​ 12.64 ​ ​ ​ ​ ​ ​ Options cancelled (51,506) ​ 15.67 ​ ​ ​ ​ ​ ​ Options expired (31,854) ​ 11.66 ​ ​ ​ ​ ​ ​ Outstanding as of March 31, 2021 9,490,381 ​ $ 15.42 5.63 ​ $ 32,322 ​ Exercisable as of March 31, 2021 6,588,157 ​ $ 14.83 4.28 ​ $ 26,310 ​ (1) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying awards and the estimated fair value of the Company’s common stock for those awards that have an exercise price below the estimated fair value at March 31, 2021. ​ For the three months ended March 31, 2021 and 2020, the Company recorded an expense of $2.4 million and $2.6 million, respectively, related to stock options granted under all plans. ​ Information relating to option grants and exercises is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ March 31, ​ ​ 2021 2020 ​ ​ (in thousands, except per share data) Weighted-average grant date fair value per option share ​ $ 7.66 ​ $ 5.33 ​ Intrinsic value of options exercised ​ 1,029 ​ 488 ​ Cash received from options exercised ​ 2,169 ​ 1,251 ​ Total fair value of the options vested during the year ​ 6,772 ​ 7,432 ​ ​ A summary of the status of the Company’s non-vested options as of March 31, 2021, and changes during the three months ended March 31, 2021, is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Grant Date ​ ​ Options ​ Fair Value Non-vested as of December 31, 2020 ​ 2,825,652 ​ $ 6.50 ​ Options granted 1,166,702 ​ ​ 7.66 ​ Options vested (1,038,624) ​ ​ 6.52 ​ Options forfeited (51,506) ​ ​ 6.77 ​ Non-vested as of March 31, 2021 2,902,224 ​ 6.96 ​ ​ As of March 31, 2021, there was $16.3 million of total unrecognized compensation cost, net of forfeitures, related to non-vested stock option based compensation arrangements granted under all plans. The cost is expected to be recognized over a weighted-average period of 3.0 years and will be adjusted for future changes in estimated forfeitures. ​ Restricted Stock Units ​ The Company grants restricted stock units, or RSUs, to certain employees and members of the Board of Directors with a vesting period of up to five years. The grantee receives one share of common stock at a specified future date for each RSU awarded. The RSUs may not be sold or otherwise transferred until certificates of common stock have been issued, recorded, and delivered to the participant. The RSUs do not have any voting or dividend rights prior to the issuance of certificates of the underlying common stock. The share-based expense associated with these grants was based on the Company’s common stock fair value at the time of grant and is amortized over the requisite service period, which generally is the vesting period using the straight-line method. During the three months ended March 31, 2021 and 2020, the Company recorded expenses of $2.2 million and $2.4 million, respectively, related to RSU awards granted under all plans. ​ As of March 31, 2021, there was $17.6 million of total unrecognized compensation cost, net of forfeitures, related to non-vested RSU-based compensation arrangements granted under all plans. The cost is expected to be recognized over a weighted-average period of 3.0 years and will be adjusted for future changes in estimated forfeitures. ​ Information relating to RSU grants and deliveries is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total Fair Market ​ ​ ​ ​ Value of RSUs ​ ​ ​ ​ Issued ​ ​ Total RSUs ​ as ​ Issued Compensation (1) ​ ​ ​ ​ (in thousands) RSUs outstanding at December 31, 2020 1,156,518 ​ ​ ​ ​ RSUs granted 496,742 ​ $ 8,936 ​ RSUs forfeited (22,627) ​ ​ ​ ​ RSUs vested (2) (416,973) ​ ​ ​ ​ RSUs outstanding at March 31, 2021 1,213,660 ​ ​ ​ ​ (1) The total fair market value is derived from the number of RSUs granted times the current stock price on the date of grant. (2) Of the vested RSUs, 161,147 shares of common stock were surrendered to fulfill tax withholding obligations. ​ The 2018 ANP Equity Incentive Plan ​ In December 2018, ANP’s board of directors approved the 2018 Plan, which is set to expire in December 2023. The 2018 Plan permits the grant of stock options and other equity awards in ANP shares to ANP employees. As of March 31, 2021, ANP granted 6,082,377 stock options to its employees under the 2018 Plan. The number of stock options outstanding as of March 31, 2021 was 5,037,280. The options vest over a period of approximately four years and have up to a 10 year contractual term. For the three months ended March 31, 2021 and 2020, the Company recorded expense of $0.1 million and $0.1 million related to stock options issued by ANP under the 2018 Plan, respectively. ​ Share-based Compensation Expense ​ The Company recorded share-based compensation expense, which is included in the Company’s condensed consolidated statement of operations as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ March 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Cost of revenues $ 1,146 $ 1,359 Operating expenses: ​ ​ ​ ​ ​ ​ Selling, distribution, and marketing ​ 127 ​ 107 General and administrative ​ 2,968 ​ 3,219 Research and development ​ 593 ​ 597 Total share-based compensation ​ $ 4,834 ​ $ 5,282 ​

Employee Benefits

Employee Benefits	3 Months Ended
	Mar. 31, 2021
Employee Benefits
Employee Benefits	Note 16. Employee Benefits ​ 401(k) Plan ​ The Company has a defined contribution 401(k) plan, or the Plan, whereby eligible employees voluntarily contribute up to a defined percentage of their annual compensation. The Company matches contributions at a rate of 50% on the first 6% of employee contributions, and pays the administrative costs of the Plan. Total employer contributions for the three months ended March 31, 2021 and 2020, were approximately $0.5 million and $0.5 million, respectively. ​ Defined Benefit Pension Plan ​ The Company’s subsidiary, AFP, has an obligation associated with a defined-benefit plan for its eligible employees. This plan provides benefits to the employees from the date of retirement and is based on the employee’s length of time employed by the Company. The calculation is based on a statistical calculation combining a number of factors that include the employee’s age, length of service, and AFP employee turnover rate. ​ The liability under the plan is based on a discount rate of 0.30% as of March 31, 2021 and December 31, 2020. The liability is included in accrued liabilities in the accompanying condensed consolidated balance sheets. The plan is currently unfunded, and the benefit obligation under the plan was $2.9 million and $3.0 million at March 31, 2021 and December 31, 2020. The Company recorded an immaterial amount of expense under the plan for the three months ended March 31, 2021 and 2020. ​ Deferred Compensation Plan ​ In December 2019, the Company established a non-qualified deferred compensation plan. The deferred compensation plan allows certain eligible participants to defer a portion of their cash compensation and provides a matching contribution at the discretion of the Company. The plan obligations are payable upon retirement, termination of employment and/or certain other times in a lump-sum distribution or in installments, as elected by the participant in accordance with the plan. Participants can allocate their deferred compensation amongst various investment options with earnings accruing to the participant. The Company has established a Rabbi Trust to fund the plan obligations and to hold the plan assets. Eligible participants began contributing to the plan in January 2020. As of March 31, 2021, the plan assets and liabilities were valued at approximately $2.0 million and $2.1 million, respectively. As of December 31, 2020, the plan assets and liabilities were valued at approximately $1.6 million and $1.7 million, respectively.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies
Commitments and Contingencies	Note 17. Commitments and Contingencies ​ Purchase Commitments ​ As of March 31, 2021, the Company has entered into commitments to purchase equipment and raw materials for an aggregate amount of approximately $52.4 million. The Company anticipates that most of these commitments with a remaining term in excess of one year will be fulfilled by 2022.

Litigation

Litigation	3 Months Ended
	Mar. 31, 2021
Litigation
Litigation	Note 18. Litigation ​ Amphastar Pharmaceuticals, Inc. v. Aventis Pharma, SA ​ In January 2009, the Company filed a qui tam ® ​ On May 11, 2017, the Company’s lawsuit against Aventis was dismissed for lack of jurisdiction. On July 14, 2017, Aventis filed an application with the District Court for entitlement to attorneys’ fees and expenses. On November 20, 2017, the District Court issued its order granting Aventis’ application for fees. ​ On November 13, 2020, the Court issued an Order (“November Order”) awarding Aventis $12.1 million in attorneys’ fees and $0.7 million in costs and expenses, and ordered Aventis to submit updated calculations on accrued interest. ​ On May 3, 2021, the Court issued a further Order based upon supplemental application to the Court seeking fees, expenses, and interest for the period after, and not covered by, the November Order. The Court awarded Aventis an additional $4.4 million bringing the total awarded Aventis to $17.2 million. ​ The Company had previously accrued $12.8 million as of December 31, 2020, based upon the November Order. As a result of the most recent ruling, the Company recorded an additional charge of $4.4 million for the three months ended March 31, 2021, in other income (expenses), in the condensed consolidated statement of operations. This amount represents management’s best estimate of the probable loss at this time. There is a reasonable possibility that the final fee award could change; however, at this time, the range of loss cannot be estimated. The Company intends to continue to vigorously defend against any imposition of attorneys’ fees and expenses in this case. ​ Regadenoson (0.4 mg/5 mL, 0.08 mg/mL) Patent Litigation ​ On February 25, 2020, Astellas US LLC, Astellas Pharma US, Inc., and Gilead Sciences, Inc. (collectively, “Astellas-Gilead”) filed a Complaint in the United States District Court for the District of Delaware against IMS for infringement of U.S. Patent Nos. 8,106,183 (the “‘183 patent”), RE47,301 (the “‘301 patent”), and 8,524,883 (the “‘883 patent”) (collectively, “Astellas-Gilead Patents”) with regard to IMS’s ANDA No. 214,252 for approval to manufacture and sell 0.4 mg/5 mL (0.08 mg/mL) intravenous solution of Regadenoson. On March 4, 2020, IMS filed its Answer and Counterclaims. On March 30, 2020, the Court issued an Order allowing the Company to join pending consolidated litigation with five other generic Regadenoson ANDA filers involving similar claims. Trial is currently scheduled for June 14, 2021. The Company’s 30-month FDA stay expires August 10, 2022. The Company intends to vigorously defend this patent lawsuit. ​ Employee Litigation ​ Brenes v. International Medication Systems, Limited ​ On September 11, 2019, a former employee, Raquel Brenes, (“Brenes”), initiated an employment litigation against IMS et al. by filing a Complaint in the Superior Court of California, Los Angeles County alleging individual and class action claims for alleged violations of various California labor laws pertaining to wage and hour, and other state laws. On September 18, 2019, Brenes filed a First Amended Complaint maintaining the individual and class action claims. ​ On January 21, 2020, Brenes filed a Second Amended Complaint that alleges only Private Attorney General Act, or PAGA, claims and omitted the individual and class action claims. On February 9, 2021, the parties reached a settlement for $1.0 million. The settlement was approved by the Court on April 7, 2021. The Company accrued the amount of $1.0 million for this litigation as of December 31, 2020. ​ Navarrette v. International Medication Systems, Limited ​ On January 30, 2020, a former employee, Robert Navarrette (“Navarrette”), provided written notice, through his counsel to IMS that he intends to file a PAGA lawsuit for alleged violation of various California labor laws pertaining to wage and hour. On April 7, 2020, Navarrette filed his PAGA lawsuit against IMS and Amphastar Pharmaceuticals, Inc. in the Superior Court of California, Los Angeles County, Central District. As to IMS, the Brenes ​ Ramirez v. Amphastar Pharmaceuticals, Inc. ​ On May 29, 2020, Priscilla Ramirez, (“Ramirez”), a former employee filed a PAGA lawsuit for alleged violations of various California labor laws pertaining to wage and hour against the Company. On April 5, 2021, the parties reached a settlement for $1.0 million. The agreement is still subject to approval by the Court. The Company accrued the amount of $1.0 million for this litigation as of March 31, 2021. ​ Other Litigation ​ The Company is also subject to various other claims, arbitrations, and lawsuits from time to time arising in the ordinary course of business. ​ The Company records a provision for contingent losses when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. In the opinion of management, the ultimate resolution of any such matters is not expected to have a material adverse effect on its financial position, results of operations, or cash flows; however, the results of litigation and claims are inherently unpredictable and the Company’s view of these matters may change in the future. Regardless of the outcome, litigation can have an adverse impact on the Company because of defense and settlement costs, diversion of management resources, and other factors.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2021
Subsequent Events
Subsequent Events	Note 19. Subsequent Events ​ In May 2021, the board of directors approved a plan for the restructuring of the equity ownership of ANP, whereby the Company will purchase an additional ownership interest in ANP from certain equity holders of ANP (the “Sellers”), and spin-off of certain subsidiaries of ANP. ​ The Company entered into three agreements relating to the restructuring of the equity ownership of ANP and its subsidiaries and the spin-off of certain subsidiaries of ANP: ​ ● The Company entered into a Share Purchase Agreement, or SPA, to acquire an additional approximately 18% of ownership interest in ANP for approximately $29.4 million from the Sellers, who had initially acquired shares in the previously disclosed July 2018 private placement, or the ANP Private Placement. ● ANP entered into a Share Repurchase Agreement, or SRA, with the Sellers and Nanjing Qianqia Enterprise Management Consulting LLP, or Qianqia, to issue shares in Hanxin, including Hanxin’s existing subsidiaries, Baixin and Letop, both of which will be included in the spin-off of Hanxin, in exchange for an additional approximately 9% of ownership interest in ANP. ● ANP entered into a Separation Agreement with Hanxin which sets forth certain assets to be held by each entity, as well as certain responsibilities and obligations of ANP and Hanxin following completion of the spin-off. ​ Upon completion of the restructuring, the Company will own approximately 85% of ANP, and ANP will retain approximately 20% of ownership interest in Hanxin. ​ Certain of the Sellers are the Company’s executive officers, directors and other related parties. The Sellers who are participating in the SPA include William J. Peters, Rong Zhou, Jacob Liawatidewi, Howard Lee, Richard Koo, Stephen Shohet, Henry Zhang, Qingqing Chen, Chongqing Zhang, Lu Zhang, and James Luo. Neither Dr. Mary Luo nor Dr. Jack Zhang are participating in the SPA. ​ The Sellers who are participating in the SRA include Dr. Mary Luo, Dr Jack Zhang, Henry Zhang, Qingqing Chen, Chongqing Zhang, Bill Zhang, and Lu Zhang. ​ As part of the restructuring, the Company will terminate the 2018 ANP Equity Incentive Plan. ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation ​ The unaudited condensed consolidated financial statements include the accounts of the Company and its subsidiaries, and are prepared in accordance with United States generally accepted accounting principles, or GAAP. Certain prior period amounts have been reclassified within the investing activities of the statement of cash flows to conform to the current period presentation. All intercompany activity has been eliminated in the preparation of the condensed consolidated financial statements. ​ 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 Biological Technology Co., Ltd., or Letop, (5) Nanjing Hanxin Pharmaceutical Technology Co., Ltd., or Hanxin, (6) Nanjing Hanxin Biomedical Testing Service Co., Ltd., or Hanxin Biomedical, (7) Nanjing Baixin Trading Co., Ltd., or Baixin, (8) Amphastar France Pharmaceuticals, S.A.S., or AFP, (9) Amphastar UK Ltd., or AUK, and (10) International Medication Systems (UK) Limited, or IMS UK. ​ In July 2018, the Company’s Chinese subsidiary, ANP, completed a private placement of its common equity interest to accredited investors and received approximately $56.3 million of cash proceeds, a portion of which was received in 2019. The Company has retained approximately 58% of the equity interest in ANP following the private placement and continues to consolidate the financial results of ANP with the Company’s results of operations. ANP’s net income after July 2, 2018, was attributed to the Company in accordance with the Company’s equity interest of approximately 58% in ANP.
COVID-19 Pandemic	COVID-19 Pandemic ​ The Company is subject to risks and uncertainties as a result of the ongoing novel coronavirus pandemic, or COVID-19. The complete extent of the impact of the COVID-19 pandemic on the Company’s business is highly uncertain and difficult to predict, as the information is constantly evolving. The Company considered the impact of COVID - ​ All of the Company’s production facilities continued to operate during the quarter as they had prior to the COVID-19 pandemic with very little change, other than for enhanced safety measures intended to prevent the spread of the virus. ​ It is not possible at this time to estimate the complete impact that COVID-19 could have on the Company’s business, including its customers and suppliers, as the impact will depend on future developments, which are highly uncertain and cannot be predicted. The Company will continue to monitor the impact of COVID-19 on all aspects of its business.
Use of Estimates	Use of Estimates ​ The preparation of condensed consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Actual results could differ from those estimates. The principal accounting estimates include: determination of allowances for credit losses, allowance for discounts, provision for chargebacks and rebates, provision for product returns, adjustment of inventory to their net realizable values, impairment of long-lived and intangible assets and goodwill, 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	Foreign Currency ​ The functional currency of the Company, its domestic subsidiaries, its Chinese subsidiary ANP, and its U.K. subsidiary, AUK, is the US Dollar. ANP maintains its books of record in Chinese yuan. These books are remeasured into the functional currency of USD using 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 condensed consolidated statements of operations. ​ The Company’s French subsidiary, AFP, maintains its book of record in euros. ANP’s subsidiaries maintain their books of record in Chinese yuan. AUK’s subsidiary, IMS UK, maintains its book of record in British pounds. These local currencies have been determined to be the subsidiaries’ respective functional currencies. These books of record 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, 2021 and 2020 were $1.5 million loss and $0.6 million loss, respectively.
Comprehensive Income (Loss)	Comprehensive Income (Loss) ​ For the three months ended March 31, 2021 and 2020, the Company included its foreign currency translation gain or loss as part of its comprehensive income (loss). No income tax expense (benefit) was allocated to other comprehensive income (loss) for the three months ended March 31, 2021 and 2020.
Advertising Expense	Advertising Expense ​ Advertising expenses, primarily associated with Primatene Mist ®
Financial Instruments	Financial Instruments ​ The carrying amounts of cash and cash equivalents, short-term investments, restricted cash and short-term investments, accounts receivable, accounts payable, accrued expenses, and short-term borrowings approximate fair value due to the short maturity of these items. The 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. 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.
Cash and Cash Equivalents	Cash and Cash Equivalents ​ Cash and cash equivalents consist of cash, money market accounts, certificates of deposit and highly liquid investments purchased with original maturities of three months or less. ​
Short-Term Investments	Short-Term Investments ​ Short-term investments as of March 31, 2021 and December 31, 2020 consisted of certificates of deposit and investment grade debt securities with original expiration dates within 12 months.
Restricted Cash	Restricted Cash ​ Restricted cash is collateral required for the Company to guarantee certain vendor payments in France. As of March 31, 2021 and December 31, 2020, the restricted cash balance was $0.2 million and $1.9 million, respectively. ​
Restricted Short-Term Investments	Restricted Short-Term Investments ​ Restricted short-term investments consist of certificates of deposit that are collateral for standby letters of credit to qualify for workers’ compensation self-insurance. The certificates of deposit have original maturities greater than three months, but less than one year. As of March 31, 2021 and December 31, 2020, the balance of restricted short-term investments was $2.2 million.
Deferred Income Taxes	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.
Recent Accounting Pronouncements	Recent Accounting Pronouncements ​ In December 2019, the Financial Accounting Standards Board, or FASB, issued Accounting Standard Update, or ASU, No. 2019-12 Simplifying the Accounting for Income Taxes (Topic 740)

Revenue Recognition (Tables)

Revenue Recognition (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue Recognition
Schedule of chargeback and rebates provision analysis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 20,380 $ 21,644 ​ Provision for chargebacks and rebates ​ 47,031 ​ 35,987 ​ Credits and payments issued to third parties ​ (46,881) ​ (39,353) ​ Ending balance ​ $ 20,530 ​ $ 18,278 ​
Schedule of product return liability analysis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 14,204 $ 10,339 ​ Provision for product returns ​ 3,233 ​ 3,099 ​ Credits issued to third parties ​ (2,517) ​ (2,239) ​ Ending balance ​ $ 14,920 ​ $ 11,199 ​

Income (Loss) per Share Attri_2

Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders (Tables)	3 Months Ended
	Mar. 31, 2021
Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders
Schedule of basic and diluted net income (loss) per share calculation	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ ​ (in thousands, except per share data) ​ Basic and dilutive numerator: ​ ​ Net income attributable to Amphastar Pharmaceuticals, Inc. ​ $ 5,041 ​ $ 3,949 ​ Denominator: ​ ​ ​ ​ ​ ​ ​ Weighted-average shares outstanding — basic ​ 47,520 ​ 46,408 ​ ​ ​ ​ ​ ​ ​ ​ ​ Net effect of dilutive securities: ​ ​ ​ ​ ​ ​ ​ Incremental shares from equity awards ​ 1,998 ​ 1,840 ​ Weighted-average shares outstanding — diluted ​ 49,518 ​ 48,248 ​ Net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders — basic ​ $ 0.11 ​ $ 0.09 ​ Net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders — diluted ​ $ 0.10 ​ $ 0.08 ​

Segment Reporting (Tables)

Segment Reporting (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting
Schedule of financial information by reporting segment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Net revenues: ​ ​ Finished pharmaceutical products ​ $ 97,882 ​ $ 81,298 ​ API ​ 5,138 ​ ​ 3,390 ​ Total net revenues ​ 103,020 ​ 84,688 ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross profit (loss): ​ ​ ​ ​ ​ ​ ​ Finished pharmaceutical products ​ 45,286 ​ 38,810 ​ API ​ (340) ​ ​ (1,987) ​ Total gross profit ​ 44,946 ​ 36,823 ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating expenses ​ 34,640 ​ 29,343 ​ ​ ​ ​ ​ ​ ​ ​ ​ Income from operations ​ 10,306 ​ 7,480 ​ Non-operating expense ​ (5,192) ​ (1,675) ​ ​ ​ ​ ​ ​ ​ ​ ​ Income before income taxes ​ $ 5,114 ​ $ 5,805 ​
Schedule of net revenues in the finished pharmaceutical products segment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Finished pharmaceutical products net revenues: ​ ​ Primatene Mist ® ​ $ 18,383 ​ $ 12,877 ​ Epinephrine ​ ​ 15,578 ​ ​ 3,990 ​ Enoxaparin ​ ​ 10,658 ​ ​ 9,168 ​ Phytonadione ​ 9,565 ​ 11,029 ​ Lidocaine ​ ​ 9,071 ​ ​ 10,657 ​ Glucagon ​ ​ 7,984 ​ ​ — ​ Naloxone ​ ​ 6,341 ​ ​ 8,875 ​ Other finished pharmaceutical products ​ 20,302 ​ 24,702 ​ Total finished pharmaceutical products net revenues ​ $ 97,882 ​ $ 81,298 ​
Schedule of depreciation and amortization expense by reporting segment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Depreciation and amortization expense ​ ​ Finished pharmaceutical products ​ $ 1,435 ​ $ 1,464 ​ API ​ 1,048 ​ 582 ​ Total depreciation and amortization expense ​ $ 2,483 ​ $ 2,046 ​
Schedule of net revenues and carrying values of long-lived assets by geographic region	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net Revenue ​ Long-Lived Assets ​ ​ Three Months Ended ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ March 31, ​ December 31, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ (in thousands) United States $ 99,170 $ 81,065 $ 125,861 $ 129,401 ​ China ​ 1,121 ​ ​ 228 ​ 97,847 ​ 98,538 ​ France ​ 2,729 ​ ​ 3,395 ​ 49,431 ​ 52,770 ​ Total ​ $ 103,020 ​ $ 84,688 ​ $ 273,139 ​ $ 280,709 ​

Customer and Supplier Concent_2

Customer and Supplier Concentration (Tables)	3 Months Ended
	Mar. 31, 2021
Customer and Supplier Concentration
Schedule of accounts receivable and net revenues by major customer	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ % of Total Accounts ​ % of Net ​ ​ ​ Receivable ​ Revenue ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ December 31, ​ March 31, ​ ​ 2021 2020 2021 2020 AmerisourceBergen 14 % 9 % 25 % 24 % McKesson 21 % 24 % 20 % 22 % Cardinal Health 16 % 17 % 15 % 19 %

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Measurements
Schedule of financial assets and liabilities measured on a recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total (Level 1) (Level 2) (Level 3) ​ ​ (in thousands) Cash equivalents - money market ​ $ 76,536 ​ $ 76,536 ​ $ — ​ $ — ​ Restricted cash - money market ​ ​ 235 ​ ​ 235 ​ ​ — ​ ​ — ​ Short-term investments - certificates of deposit ​ ​ 9,284 ​ ​ — ​ ​ 9,284 ​ ​ — ​ Restricted short-term investments - certificates of deposit ​ 2,200 ​ — ​ 2,200 ​ — ​ Corporate and municipal bonds ​ ​ 4,199 ​ ​ — ​ ​ 4,199 ​ ​ — ​ Interest rate swap liabilities related to variable rate loans ​ ​ (723) ​ ​ — ​ ​ (723) ​ ​ — ​ Fair value measurement as of March 31, 2021 ​ $ 91,731 ​ $ 76,771 ​ $ 14,960 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents - money market ​ $ 58,710 ​ $ 58,710 ​ $ — ​ $ — ​ Restricted cash - money market ​ ​ 1,865 ​ ​ 1,865 ​ ​ — ​ ​ — ​ Short-term investments - certificates of deposit ​ ​ 9,089 ​ ​ — ​ ​ 9,089 ​ ​ — ​ Restricted short-term investments - certificates of deposit ​ 2,200 ​ — ​ 2,200 ​ — ​ Corporate and municipal bonds ​ ​ 3,855 ​ ​ — ​ ​ 3,855 ​ ​ — ​ Interest rate swap liabilities related to variable rate loans ​ ​ (902) ​ ​ — ​ ​ (902) ​ ​ — ​ Fair value measurement as of December 31, 2020 ​ $ 74,817 ​ $ 60,575 ​ $ 14,242 ​ $ — ​

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2021
Investments
Schedule of securities classified as held-to-maturity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) Corporate bonds ​ $ 1,053 ​ $ — ​ $ (1) ​ $ 1,052 Municipal bonds ​ ​ 3,148 ​ ​ — ​ ​ (1) ​ ​ 3,147 Total investments as of March 31, 2021 ​ $ 4,201 ​ $ — ​ $ (2) ​ $ 4,199 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate bonds ​ $ 1,560 ​ $ — ​ $ (1) ​ $ 1,559 Municipal bonds ​ ​ 2,297 ​ ​ — ​ ​ (1) ​ ​ 2,296 Total investments as of December 31, 2020 ​ $ 3,857 ​ $ — ​ $ (2) ​ $ 3,855

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets
Schedule of weighted-average life, original cost, accumulated amortization and net book value by major class	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Accumulated ​ ​ ​ ​ Life (Years) Original Cost Amortization Net Book Value ​ ​ (in thousands) Definite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ IMS (UK) international product rights ​ 10 ​ $ 9,640 ​ $ 4,499 ​ $ 5,141 ​ Patents 12 ​ 486 ​ ​ 308 ​ 178 ​ Land-use rights 39 ​ 2,540 ​ ​ 634 ​ 1,906 ​ Subtotal 12 ​ 12,666 ​ 5,441 ​ 7,225 ​ Indefinite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Trademark * ​ 29,225 ​ — ​ 29,225 ​ Goodwill - Finished pharmaceutical products * ​ 3,793 ​ — ​ 3,793 ​ Subtotal * ​ 33,018 ​ — ​ 33,018 ​ As of March 31, 2021 * ​ $ 45,684 ​ $ 5,441 ​ $ 40,243 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Accumulated ​ ​ ​ ​ Life (Years) Original Cost Amortization Net Book Value ​ ​ (in thousands) Definite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ IMS (UK) international product rights ​ 10 ​ $ 9,561 ​ $ 4,223 ​ $ 5,338 ​ Patents 12 ​ 486 ​ ​ 297 ​ 189 ​ Land-use rights 39 ​ 2,540 ​ ​ 617 ​ 1,923 ​ Subtotal 12 ​ 12,587 ​ 5,137 ​ 7,450 ​ Indefinite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Trademark * ​ 29,225 ​ — ​ 29,225 ​ Goodwill - Finished pharmaceutical products * ​ 3,940 ​ — ​ 3,940 ​ Subtotal * ​ 33,165 ​ — ​ 33,165 ​ As of December 31, 2020 * ​ $ 45,752 ​ $ 5,137 ​ $ 40,615 ​ * Intangible assets with indefinite lives have an indeterminable average life.
Schedule of changes in carrying amounts of goodwill	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 3,940 $ 3,634 ​ Currency translation ​ (147) ​ 306 ​ Ending balance ​ $ 3,793 ​ $ 3,940 ​

Inventories (Tables)

Inventories (Tables)	3 Months Ended
	Mar. 31, 2021
Inventories
Schedule of inventories	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Raw materials and supplies $ 43,258 $ 47,051 ​ Work in process ​ 35,081 ​ 37,257 ​ Finished goods ​ 18,771 ​ 12,523 ​ Total inventories ​ $ 97,110 ​ $ 96,831 ​

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	3 Months Ended
	Mar. 31, 2021
Property, Plant, and Equipment
Schedule of property, plant, and equipment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Buildings $ 124,952 $ 124,326 ​ Leasehold improvements ​ 30,093 ​ 30,028 ​ Land ​ 7,659 ​ 7,719 ​ Machinery and equipment ​ 210,776 ​ 211,666 ​ Furniture, fixtures, and automobiles ​ 26,862 ​ 26,482 ​ Construction in progress ​ 42,165 ​ 43,981 ​ Total property, plant, and equipment ​ 442,507 ​ 444,202 ​ Less accumulated depreciation ​ (189,242) ​ (184,147) ​ Total property, plant, and equipment, net ​ $ 253,265 ​ $ 260,055 ​

Accounts Payable and Accrued _2

Accounts Payable and Accrued Liabilities (Tables)	3 Months Ended
	Mar. 31, 2021
Accounts Payable and Accrued Liabilities.
Schedule of accounts payable and accrued liabilities	​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ 2021 ​ 2020 ​ (in thousands) Accrued customer fees and rebates $ 10,466 ​ $ 9,029 Accrued payroll and related benefits ​ 26,742 ​ ​ 24,597 Accrued product returns, current portion ​ 10,676 ​ ​ 10,190 Accrued loss on firm purchase commitments ​ 8,625 ​ ​ 1,223 Accrued litigation and settlements ​ 19,449 ​ ​ 13,780 Other accrued liabilities ​ 9,600 ​ ​ 12,328 Total accrued liabilities 85,558 ​ 71,147 Accounts payable 22,987 ​ 24,357 Total accounts payable and accrued liabilities $ 108,545 ​ $ 95,504

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2021
Debt
Schedule of debt	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Line of Credit Facilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Line of credit facility with China Everbright Bank due June 2021 ​ $ 763 ​ $ 764 ​ Line of credit facility with China Merchant Bank due August 2021 ​ ​ 381 ​ ​ 382 ​ Line of credit facility with Bank of Nanjing due October 2021 ​ ​ 153 ​ ​ 153 ​ Line of credit facility with Cathay Bank due May 2022 ​ — ​ — ​ Line of credit facility with East West Bank due December 2022 ​ ​ — ​ ​ — ​ Equipment line of credit facility with East West Bank due September 2025 ​ ​ 3,216 ​ ​ 3,216 ​ ​ ​ ​ ​ ​ ​ ​ ​ Mortgage Loans ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mortgage payable with East West Bank due May 2021 ​ ​ 3,282 ​ ​ 3,306 ​ Mortgage payable with East West Bank due October 2026 ​ ​ 3,317 ​ ​ 3,334 ​ Mortgage payable with East West Bank due June 2027 ​ ​ 8,472 ​ ​ 8,510 ​ Mortgage payable with Cathay Bank due August 2027 ​ 7,220 ​ 7,268 ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment Loans ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment loan with East West Bank due June 2021 ​ ​ 306 ​ ​ 612 ​ Equipment loan with East West Bank due December 2022 ​ ​ 3,500 ​ ​ 4,000 ​ Equipment loan with East West Bank due February 2024 ​ ​ 4,839 ​ ​ 5,254 ​ ​ ​ ​ ​ ​ ​ ​ ​ Other Loans and Payment Obligations ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Acquisition loan with Cathay Bank due June 2024 ​ 8,137 ​ 8,710 ​ French government loan due July 2021 ​ ​ 64 ​ ​ 64 ​ French government loans due December 2026 ​ ​ 338 ​ ​ 350 ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment under Finance Leases ​ 519 ​ 526 ​ Total debt ​ 44,507 ​ 46,449 ​ Less current portion of long-term debt ​ 12,173 ​ 12,263 ​ Long-term debt, net of current portion ​ $ 32,334 ​ $ 34,186 ​

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2021
Income Taxes
Schedule of reconciliation of the statutory federal income tax rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ March 31, ​ ​ 2021 2020 ​ ​ (in thousands) ​ Income before taxes ​ $ 5,114 ​ $ 5,805 ​ Income tax provision ​ ​ 1,155 ​ 2,280 ​ Net income ​ $ 3,959 ​ $ 3,525 ​ Income tax provision as a percentage of income before income taxes ​ ​ 22.6 % 39.3 %

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2021
Stockholders' Equity
Schedule of key assumptions to determine fair value of options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ ​ ​ March 31, ​ ​ ​ 2021 2020 ​ Average volatility 42.2 % 43.0 % ​ Average risk-free interest rate 1.3 % 0.8 % ​ Weighted-average expected life in years 6.3 ​ 5.8 ​ ​ Dividend yield rate — % — % ​
Schedule of the summary of option activity under all plans	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ Remaining ​ Aggregate ​ ​ ​ ​ Exercise ​ Contractual ​ Intrinsic ​ ​ Options ​ Price ​ Term (Years) ​ Value (1) ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) Outstanding as of December 31, 2020 8,580,475 $ 15.00 ​ ​ Options granted 1,166,702 ​ 17.99 ​ ​ ​ ​ ​ ​ Options exercised (173,436) ​ 12.64 ​ ​ ​ ​ ​ ​ Options cancelled (51,506) ​ 15.67 ​ ​ ​ ​ ​ ​ Options expired (31,854) ​ 11.66 ​ ​ ​ ​ ​ ​ Outstanding as of March 31, 2021 9,490,381 ​ $ 15.42 5.63 ​ $ 32,322 ​ Exercisable as of March 31, 2021 6,588,157 ​ $ 14.83 4.28 ​ $ 26,310 ​ (1) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying awards and the estimated fair value of the Company’s common stock for those awards that have an exercise price below the estimated fair value at March 31, 2021.
Schedule of information relating to options grants	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ March 31, ​ ​ 2021 2020 ​ ​ (in thousands, except per share data) Weighted-average grant date fair value per option share ​ $ 7.66 ​ $ 5.33 ​ Intrinsic value of options exercised ​ 1,029 ​ 488 ​ Cash received from options exercised ​ 2,169 ​ 1,251 ​ Total fair value of the options vested during the year ​ 6,772 ​ 7,432 ​
Schedule of the summary of nonvested options status	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ Grant Date ​ ​ Options ​ Fair Value Non-vested as of December 31, 2020 ​ 2,825,652 ​ $ 6.50 ​ Options granted 1,166,702 ​ ​ 7.66 ​ Options vested (1,038,624) ​ ​ 6.52 ​ Options forfeited (51,506) ​ ​ 6.77 ​ Non-vested as of March 31, 2021 2,902,224 ​ 6.96 ​
Schedule of information relating to RSU grants and deliveries	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total Fair Market ​ ​ ​ ​ Value of RSUs ​ ​ ​ ​ Issued ​ ​ Total RSUs ​ as ​ Issued Compensation (1) ​ ​ ​ ​ (in thousands) RSUs outstanding at December 31, 2020 1,156,518 ​ ​ ​ ​ RSUs granted 496,742 ​ $ 8,936 ​ RSUs forfeited (22,627) ​ ​ ​ ​ RSUs vested (2) (416,973) ​ ​ ​ ​ RSUs outstanding at March 31, 2021 1,213,660 ​ ​ ​ ​ (1) The total fair market value is derived from the number of RSUs granted times the current stock price on the date of grant. (2) Of the vested RSUs, 161,147 shares of common stock were surrendered to fulfill tax withholding obligations.
Schedule of recorded share-based compensation expense under all plans	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ March 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Cost of revenues $ 1,146 $ 1,359 Operating expenses: ​ ​ ​ ​ ​ ​ Selling, distribution, and marketing ​ 127 ​ 107 General and administrative ​ 2,968 ​ 3,219 Research and development ​ 593 ​ 597 Total share-based compensation ​ $ 4,834 ​ $ 5,282

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jul. 31, 2018	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Gains and (losses) of intercompany foreign currency transactions		$ (1,500)	$ (600)
Income tax expense allocated to other comprehensive income		0	0
Selling, distribution, and marketing expense		4,537	3,294
Restricted cash		235		$ 1,865
Certificates of deposit		2,200		$ 2,200
ANP
Proceeds from private placement	$ 56,300
Equity interest retained post private placement	58.00%
Finished Pharmaceutical Products | Primatene Mist
Advertising expense		$ 2,200	$ 1,000

Revenue Recognition (Analysis o

Revenue Recognition (Analysis of the Chargeback Provision) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Beginning balance	$ 20,380	$ 21,644	$ 21,644
Provision for chargebacks and rebates	47,031	35,987
Credits and payments issued to third parties	(46,881)	(39,353)
Ending balance	20,530	$ 18,278	20,380
Accounts Receivable, Net
Provision for chargebacks and rebates	16,400		16,400
Accounts Payable and Accrued Liabilities
Provision for chargebacks and rebates	$ 4,100		$ 4,000

Revenue Recognition (Analysis_2

Revenue Recognition (Analysis of Product Return Liability) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Aggregate product return rate	1.40%	1.10%
Return accrual included in accounts payable and accrued liabilities	$ 10,676		$ 10,190
Return accrual included in other long-term liabilities	4,200		$ 4,000
Product returns
Beginning balance	14,204	$ 10,339
Provision for product returns	3,233	3,099
Credits issued to third parties	(2,517)	(2,239)
Ending balance	$ 14,920	$ 11,199

Income (Loss) per Share Attri_3

Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders (Narrative) (Details) - Stock Options - $ / shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Shares	1,899,833	1,999,083
Antidilutive Securities Excluded from Computation of Earnings Per Share, Exercise Price of Excluded Securities	$ 20.85	$ 20.81

Income (Loss) per Share Attri_4

Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders (Calculation of Basic and Diluted Net Income (Loss) Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Basic and dilutive numerator:
Net Income (Loss) Attributable to Parent	$ 5,041	$ 3,949
Denominator:
Weighted-average shares outstanding-basic	47,520	46,408
Net effect of dilutive securities:
Incremental shares from equity awards	1,998	1,840
Weighted-average shares outstanding - diluted	49,518	48,248
Net income (loss) per share - basic	$ 0.11	$ 0.09
Net income (loss) per share - diluted	$ 0.10	$ 0.08

Segment Reporting (Selected Fin

Segment Reporting (Selected Financial Information by Reporting Segment) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)segment	Mar. 31, 2020USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment	2
Net revenues:
Net Revenue	$ 103,020	$ 84,688
Gross profit (loss):
Gross Profit	44,946	36,823
Operating expenses	34,640	29,343
Income (loss) from operations	10,306	7,480
Non-operating income (expenses)	(5,192)	(1,675)
Income (loss) before income taxes	5,114	5,805
Finished Pharmaceutical Products
Net revenues:
Net Revenue	97,882	81,298
Gross profit (loss):
Gross Profit	45,286	38,810
API
Net revenues:
Net Revenue	5,138	3,390
Gross profit (loss):
Gross Profit	$ (340)	$ (1,987)

Segment Reporting (Summary of N

Segment Reporting (Summary of Net Revenues by Product Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net Revenue	$ 103,020	$ 84,688
Finished Pharmaceutical Products
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net Revenue	97,882	81,298
Finished Pharmaceutical Products | Enoxaparin
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net Revenue	10,658	9,168
Finished Pharmaceutical Products | Lidocaine
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net Revenue	9,071	10,657
Finished Pharmaceutical Products | Phytonadione
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net Revenue	9,565	11,029
Finished Pharmaceutical Products | Naloxone
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net Revenue	6,341	8,875
Finished Pharmaceutical Products | Epinephrine
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net Revenue	15,578	3,990
Finished Pharmaceutical Products | Primatene Mist
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net Revenue	18,383	12,877
Finished Pharmaceutical Products | Glucagon
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net Revenue	7,984
Finished Pharmaceutical Products | Other Finished Pharmaceutical Products
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net Revenue	$ 20,302	$ 24,702

Segment Reporting (Depreciation

Segment Reporting (Depreciation and Amortization Expense by Reporting Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Depreciation and amortization expense	$ 2,483	$ 2,046
Finished Pharmaceutical Products
Segment Reporting Information [Line Items]
Depreciation and amortization expense	1,435	1,464
API
Segment Reporting Information [Line Items]
Depreciation and amortization expense	$ 1,048	$ 582

Segment Reporting (Summary of R

Segment Reporting (Summary of Revenues and Long-Lived Assets by Geographic Region) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]
Net Revenue	$ 103,020	$ 84,688
Long-Lived Assets	273,139		$ 280,709
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Net Revenue	99,170	81,065
Long-Lived Assets	125,861		129,401
CHINA
Revenues from External Customers and Long-Lived Assets [Line Items]
Net Revenue	1,121	228
Long-Lived Assets	97,847		98,538
FRANCE
Revenues from External Customers and Long-Lived Assets [Line Items]
Net Revenue	2,729	$ 3,395
Long-Lived Assets	$ 49,431		$ 52,770

Customer and Supplier Concent_3

Customer and Supplier Concentration (Details) - Customer Concentration Risk [Member] - item	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Revenue, Major Customer [Line Items]
Number of major customers that are wholesale distributors	3
Accounts Receivable, Net
Revenue, Major Customer [Line Items]
Number of major customers	3		3
Net Revenues
Revenue, Major Customer [Line Items]
Number of major customers	3	3
AmerisourceBergen | Accounts Receivable, Net
Revenue, Major Customer [Line Items]
Major Customers	14.00%		9.00%
AmerisourceBergen | Net Revenues
Revenue, Major Customer [Line Items]
Major Customers	25.00%	24.00%
Cardinal Health | Accounts Receivable, Net
Revenue, Major Customer [Line Items]
Major Customers	16.00%		17.00%
Cardinal Health | Net Revenues
Revenue, Major Customer [Line Items]
Major Customers	15.00%	19.00%
McKesson | Accounts Receivable, Net
Revenue, Major Customer [Line Items]
Major Customers	21.00%		24.00%
McKesson | Net Revenues
Revenue, Major Customer [Line Items]
Major Customers	20.00%	22.00%

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Values of the Company's Financial Assets and Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement	$ 91,731	$ 74,817
Recurring Basis | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps related to variable rate loans	(723)	(902)
Recurring Basis | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate and municipal bonds	4,199	3,855
Recurring Basis | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	9,284	9,089
Restricted short-term investments	2,200	2,200
Recurring Basis | Money market
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	76,536	58,710
Restricted cash	235	1,865
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement	76,771	60,575
Level 1 | Money market
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	76,536	58,710
Restricted cash	235	1,865
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement	14,960	14,242
Level 2 | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps related to variable rate loans	(723)	(902)
Level 2 | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate and municipal bonds	4,199	3,855
Level 2 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	9,284	9,089
Restricted short-term investments	$ 2,200	$ 2,200

Investments (Held-to_Maturity)

Investments (Held-to_Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 4,201	$ 3,857
Gross Unrealized Losses	(2)	(2)
Fair Value	4,199	3,855
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,053	1,560
Gross Unrealized Losses	(1)	(1)
Fair Value	1,052	1,559
Municipal Bonds [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,148	2,297
Gross Unrealized Losses	(1)	(1)
Fair Value	$ 3,147	$ 2,296

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets (Summary of Intangible Assets) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Definite-lived intangible assets
Weighted-Average Life (Years)	12 years	12 years
Finite-Lived Intangible Assets, Gross	$ 12,666	$ 12,587
Accumulated Amortization	5,441	5,137
Finite-Lived Intangible Assets, Net	7,225	7,450
Indefinite-lived intangible assets
Goodwill recognized	3,793	3,940	$ 3,634
Subtotal, Original Cost	33,018	33,165
Subtotal, Net Book Value	33,018	33,165
Balance, Original Cost	45,684	45,752
Balance, Net Book Value	40,243	40,615
Finished Pharmaceutical Products
Indefinite-lived intangible assets
Goodwill recognized	3,793	3,940
Trademarks
Indefinite-lived intangible assets
Indefinite-lived intangible assets	$ 29,225	$ 29,225
Patents
Definite-lived intangible assets
Weighted-Average Life (Years)	12 years	12 years
Finite-Lived Intangible Assets, Gross	$ 486	$ 486
Accumulated Amortization	308	297
Finite-Lived Intangible Assets, Net	$ 178	$ 189
Land-use rights
Definite-lived intangible assets
Weighted-Average Life (Years)	39 years	39 years
Finite-Lived Intangible Assets, Gross	$ 2,540	$ 2,540
Accumulated Amortization	634	617
Finite-Lived Intangible Assets, Net	$ 1,906	$ 1,923
International Medication Systems (UK) Limited | Acquired international product rights
Definite-lived intangible assets
Weighted-Average Life (Years)	10 years	10 years
Finite-Lived Intangible Assets, Gross	$ 9,640	$ 9,561
Accumulated Amortization	4,499	4,223
Finite-Lived Intangible Assets, Net	$ 5,141	$ 5,338

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets (Summary of Changes in the Carrying Amount of Goodwill) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Goodwill and Intangible Assets
Beginning balance	$ 3,940	$ 3,634
Currency translation and other adjustments	(147)	306
Ending balance	$ 3,793	$ 3,940

Inventories (Details)

Inventories (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Raw materials and supplies	$ 43,258		$ 47,051
Work in process	35,081		37,257
Finished goods	18,771		12,523
Total inventory, net	97,110		$ 96,831
Inventory adjustment to reflect net realizable value	9,500	$ 2,100
Enoxaparin
Inventory, Firm Purchase Commitment, Loss	$ 8,600	$ 2,100

Property, Plant, and Equipmen_2

Property, Plant, and Equipment (Summary of Property, Plant, and Equipment) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	$ 442,507	$ 444,202
Less accumulated depreciation and amortization	(189,242)	(184,147)
Total property, plant, and equipment, net	253,265	260,055
Buildings
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	124,952	124,326
Leasehold improvement
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	30,093	30,028
Land
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	7,659	7,719
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	210,776	211,666
Furniture, fixtures, and automobiles
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	26,862	26,482
Construction in progress
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	$ 42,165	$ 43,981

Accounts Payable and Accrued _3

Accounts Payable and Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accounts Payable and Accrued Liabilities.
Accrued customer fees and rebates	$ 10,466	$ 9,029
Accrued payroll and related benefits	26,742	24,597
Accrued product returns, current portion	10,676	10,190
Accrued loss on firm purchase commitments	8,625	1,223
Accrued litigation settlement	19,449	13,780
Other accrued liabilities	9,600	12,328
Total accrued liabilities	85,558	71,147
Accounts payable	22,987	24,357
Total accounts payable and accrued liabilities	$ 108,545	$ 95,504

Debt (Schedule of Debt) (Detail

Debt (Schedule of Debt) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument
Equipment under Finance Leases	$ 519	$ 526
Total debt	44,507	46,449
Less current portion of long-term debt and finance leases	12,173	12,263
Long-term debt and finance leases, net of current portion	32,334	34,186
Mortgage Payable - Due May 2021 | East West Bank
Debt Instrument
Long Term Debt	3,282	3,306
Equipment Loan - Due June 2021 | East West Bank
Debt Instrument
Long Term Debt	306	612
Equipment Loan - Due December 2022 | East West Bank
Debt Instrument
Long Term Debt	3,500	4,000
Equipment Loan - Due February 2024 | East West Bank
Debt Instrument
Long Term Debt	4,839	5,254
Mortgage Payable - Due October 2026 | East West Bank
Debt Instrument
Long Term Debt	3,317	3,334
Mortgage Payable - Due June 2027 | East West Bank
Debt Instrument
Long Term Debt	8,472	8,510
Mortgage Payable - Due August 2027 | Cathay Bank
Debt Instrument
Long Term Debt	7,220	7,268
Acquisition Loan - Due June 2024 | Cathay Bank
Debt Instrument
Long Term Debt	8,137	8,710
Line of credit - Due June 2021 | China Everbright Bank
Debt Instrument
Long Term Debt	763	764
Line of Credit - Due August 2021 | China Merchant Bank
Debt Instrument
Long Term Debt	381	382
Line of Credit - Due October 2021 | Bank of Nanjing
Debt Instrument
Long Term Debt	153	153
Equipment Line of Credit - Due September 2025 | East West Bank
Debt Instrument
Long Term Debt	3,216	3,216
French Government Loan - Due July 2021 | Seine-Normandie Water Agency
Debt Instrument
Long Term Debt	64	64
French Government Loan 4 - Due December 2026 | Seine-Normandie Water Agency
Debt Instrument
Long Term Debt	$ 338	$ 350

Income Taxes (Summary of Income

Income Taxes (Summary of Income Before Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income (loss) before income taxes:
Income (loss) before income taxes	$ 5,114	$ 5,805
Income tax provision (benefit)	1,155	2,280
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 3,959	$ 3,525
Income tax provision as a percentage of income before income taxes	22.60%	39.30%
Other Effective Tax Rate Provision (Benefit)	$ 100	$ 200

Stockholders' Equity (Share Buy

Stockholders' Equity (Share Buyback Program) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Aug. 04, 2020
Equity, Class of Treasury Stock [Line Items]
Treasury Stock, Value, Acquired, Cost Method	$ 3,783	$ 10,950
November 2014 Share Repurchase Plan
Equity, Class of Treasury Stock [Line Items]
Increase authorized for share buyback program			$ 20,000
Treasury Stock, Shares, Acquired (in Shares)	204,698	646,715
Treasury Stock, Value, Acquired, Cost Method	$ 3,800	$ 10,900

Stockholders' Equity (The 2015

Stockholders' Equity (The 2015 Equity Incentive Plan) (Details) - The 2015 Equity Incentive Plan - shares	1 Months Ended
	Jan. 31, 2021	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in Shares)		6,181,926
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	1,187,386

Stockholders' Equity (2014 Empl

Stockholders' Equity (2014 Employee Stock Purchase Plan) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	$ 4,834	$ 5,282
2014 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Shares, Employee Stock Purchase Plans (in Shares)	807,550
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in Shares)	1,192,450
Allocated share based compensation	$ 100	$ 100

Stockholders' Equity (Key Assum

Stockholders' Equity (Key Assumptions Used in Determining Fair Value of Options Granted) (Details)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Stockholders' Equity
Average volatility	42.20%	43.00%
Risk-free interest rate	1.30%	0.80%
Weighted-average expected life in years	6 years 3 months 18 days	5 years 9 months 18 days
Dividend yield rate	0.00%	0.00%

Stockholders' Equity (Summary o

Stockholders' Equity (Summary of Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Options
Outstanding Options, Beginning of period	8,580,475
Options granted	1,166,702
Options exercised	(173,436)
Options cancelled	(51,506)
Options expired	(31,854)
Outstanding Options, End of period	9,490,381
Exercisable at the end of period	6,588,157
Weighted-Average Exercise Price
Outstanding Exercise Price (in dollars per share)	$ 15
Options granted (in dollars per share)	17.99
Options exercised (in dollars per share)	12.64
Options cancelled (in dollars per share)	15.67
Options expired (in dollars per share)	11.66
Outstanding Exercise Price (in dollars per share)	15.42
Exercisable at the end of period (in dollars per share)	$ 14.83
Additional Disclosures
Outstanding Intrinsic Value	$ 32,322
Exercisable aggregate intrinsic value	26,310
Allocated share based compensation	$ 4,834	$ 5,282
Employee Stock Option
Additional Disclosures
Outstanding Contractual Term (in Years)	5 years 7 months 17 days
Exercisable remaining contractual term (in Years)	4 years 3 months 10 days
Allocated share based compensation	$ 2,400	$ 2,600

Stockholders' Equity (Informati

Stockholders' Equity (Information Relating to Option Grants and Exercises) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Stockholders' Equity
Weighted-average grant date fair value (in Dollars per share)	$ 7.66	$ 5.33
Intrinsic value of options exercised	$ 1,029	$ 488
Cash received	2,169	1,251
Total fair value of the options vested during the year	$ 6,772	$ 7,432

Stockholders' Equity (Summary_2

Stockholders' Equity (Summary of Nonvested Options) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Options
Nonvested at beginning of period	2,825,652
Options granted	1,166,702
Options vested	(1,038,624)
Options forfeited	(51,506)
Nonvested at end of period	2,902,224
Weighted-Average Grant Date Fair Value
Nonvested at beginning of period (in dollars per share)	$ 6.50
Options granted (in dollars per share)	7.66	$ 5.33
Options vested (in dollars per share)	6.52
Options forfeited (in dollars per share)	6.77
Nonvested at end of period (in dollars per share)	$ 6.96
Employee Consultant And Directors Stock Options
Weighted-Average Grant Date Fair Value
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options	$ 16.3
Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	3 years

Stockholders' Equity (Restricte

Stockholders' Equity (Restricted Stock Units) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	$ 4,834	$ 5,282
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	5 years
Allocated share based compensation	$ 2,200	$ 2,400
Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Restricted Stock Units, Number of Shares of Common Stock Per Award (in Shares)	1
Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 17,600

Stockholders' Equity (Informa_2

Stockholders' Equity (Information Relating to RSU Grants and Deliveries) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)shares
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Total RSUs outstanding at the beginning of the period	1,156,518
RSUs granted	496,742
RSUs forfeited	(22,627)
RSUs vested	(416,973)
Total RSUs outstanding at the end of the period	1,213,660
Stock surrendered to fulfill tax withholding obligations	161,147
Restricted Stock Units Issued as Compensation
Total Fair Market Value of RSUs Issued
RSUs granted (in Dollars) | $	$ 8,936

Stockholders' Equity (The 2018

Stockholders' Equity (The 2018 ANP Equity Incentive Plan) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jun. 30, 2019	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted		1,166,702
Outstanding Options, End of period		9,490,381
Allocated share based compensation		$ 4,834	$ 5,282
The 2018 ANP Equity Incentive Plan | Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted		6,082,377
Outstanding Options, End of period		5,037,280
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	10 years
Allocated share based compensation		$ 100	$ 100

Stockholders' Equity (Share-Bas

Stockholders' Equity (Share-Based Compensation Expense Included in the Statement of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	$ 4,834	$ 5,282
Cost of revenues
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	1,146	1,359
Selling, distribution and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	127	107
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	2,968	3,219
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	$ 593	$ 597

Employee Benefits (Details)

Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Employee Benefits
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	50.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	6.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 0.5	$ 0.5
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	0.30%		0.30%
Defined Benefit Plan, Benefit Obligation	$ 2.9		$ 3
Pension Cost	0	$ 0
Deferred compensation plan assets	2		1.6
Deferred compensation plan liabilities	$ 2.1		$ 1.7

Commitments and Contingencies (

Commitments and Contingencies (Purchase Commitments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Contractual Obligation	$ 44,507	$ 46,449
Commitments to Purchase Equipment and Raw Materials
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Long-term Purchase Commitment, Amount	$ 52,400

Litigation (Details)

Litigation (Details) - USD ($) $ in Thousands	May 03, 2021	Apr. 05, 2021	Feb. 09, 2021	Nov. 13, 2020	May 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Estimated Litigation Liability						$ 19,449	$ 13,780
Brenes vs International Medication Systems, Limited
Loss Contingencies [Line Items]
Litigation Settlement, Amount			$ 1,000
Estimated Litigation Liability							1,000
Amphastar Pharmaceuticals, Inc. Vs Aventis Pharma, SA
Loss Contingencies [Line Items]
Estimated Litigation Liability						4,400	$ 12,800
Amphastar Pharmaceuticals, Inc. Vs Aventis Pharma, SA | Subsequent Event
Loss Contingencies [Line Items]
Litigation Settlement, Amount	$ 4,400				$ 17,200
Settled Litigation [Member] | Ramirez vs Amphastar Pharmaceuticals, Inc
Loss Contingencies [Line Items]
Estimated Litigation Liability						$ 1,000
Settled Litigation [Member] | Ramirez vs Amphastar Pharmaceuticals, Inc | Subsequent Event
Loss Contingencies [Line Items]
Litigation Settlement, Amount		$ 1,000
Settled Litigation [Member] | Amphastar Pharmaceuticals, Inc. Vs Aventis Pharma, SA
Loss Contingencies [Line Items]
Litigation Settlement, Amount				$ 12,100
Costs and expenses				$ 700

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent Event $ in Millions	1 Months Ended
	May 31, 2021USD ($)
Hanxin
Subsequent Event
Ownership after transaction	20.00%
ANP
Subsequent Event
Percentage of ownership interest acquired	18.00%
Payments for additional ownership interest	$ 29.4
Percentage of additional ownership interest from shares repurchase	9.00%
Ownership percentage	85.00%