Amphastar Pharmaceuticals (AMPH) 10-Q 9 Nov 21 2021 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 02, 2021
Document and Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 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		47,849,145
Entity Central Index Key	0001297184
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current Assets:
Cash and cash equivalents	$ 106,610	$ 92,642
Restricted cash	235	1,865
Short-term investments	8,021	12,977
Restricted short-term investments	2,200	2,200
Accounts receivable, net	78,090	66,005
Inventories	100,240	96,831
Income tax refunds and deposits	520	385
Prepaid expenses and other assets	7,755	6,777
Total current assets	303,671	279,682
Property, plant, and equipment, net	242,924	260,055
Finance lease right-of-use assets	428	612
Operating lease right-of-use assets	27,663	20,042
Equity method investment	4,193
Goodwill and intangible assets, net	39,192	40,615
Other assets	11,610	5,250
Deferred tax assets	21,996	24,980
Total assets	651,677	631,236
Current Liabilities:
Accounts payable and accrued liabilities	88,911	95,504
Income taxes payable	3,960	1,077
Current portion of long-term debt	2,256	12,263
Current portion of operating lease liabilities	2,862	3,357
Total current liabilities	97,989	112,201
Long-term reserve for income tax liabilities	4,709	4,709
Long-term debt, net of current portion and unamortized debt costs	75,552	34,186
Long-term operating lease liabilities, net of current portion	25,466	17,464
Deferred tax liabilities	2,901	741
Other long-term liabilities	14,884	13,212
Total liabilities	221,501	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; 56,051,662 and 47,982,690 shares issued and outstanding as of September 30, 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	412,917	410,061
Retained earnings	160,577	117,773
Accumulated other comprehensive loss	(6,277)	(3,721)
Treasury stock	(137,047)	(121,812)
Total Amphastar Pharmaceuticals, Inc. stockholders' equity	430,176	402,306
Non-controlling Interests		46,417
Total equity	430,176	448,723
Total liabilities and stockholders' equity	$ 651,677	$ 631,236

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 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	56,051,662	54,760,922
Common stock; shares outstanding	47,982,690	47,495,439

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
CONSOLIDATED STATEMENTS OF OPERATIONS
Net revenues	$ 112,198	$ 83,431	$ 316,881	$ 253,925
Cost of revenues	61,015	46,923	173,376	147,417
Gross profit	51,183	36,508	143,505	106,508
Operating (income) expenses:
Selling, distribution, and marketing	4,745	3,673	13,411	10,993
General and administrative	10,910	11,674	40,813	38,344
Research and development	10,759	17,644	43,646	49,096
Total operating expenses	26,414	32,991	97,870	98,433
Income (loss) from operations	24,769	3,517	45,635	8,075
Non-operating (expenses) income:
Interest income	141	161	444	512
Interest expense	(527)	(175)	(717)	(286)
Other income (expenses), net	13,263	3,575	11,615	3,078
Total non-operating (expenses) income, net	12,877	3,561	11,342	3,304
Income (loss) before income taxes	37,646	7,078	56,977	11,379
Income tax provision (benefit)	6,686	2,285	13,436	4,490
Net income (loss)	30,960	4,793	43,541	6,889
Net income (loss) attributable to non-controlling interests	1,412	874	1,185	(787)
Net income (loss) attributable to Amphastar Pharmaceuticals, Inc.	$ 29,548	$ 3,919	$ 42,356	$ 7,676
Net income (loss) per share attributable to Amphastar Pharmaceuticals, Inc. stockholders:
Basic (in Dollars per share)	$ 0.62	$ 0.08	$ 0.89	$ 0.16
Diluted (in Dollars per share)	$ 0.59	$ 0.08	$ 0.85	$ 0.16
Weighted-average shares used to compute net income (loss) per share attributable to Amphastar Pharmaceuticals, Inc. stockholders:
Basic (in Shares)	48,022	47,496	47,758	46,886
Diluted (in Shares)	50,009	49,848	49,693	48,922

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss) attributable to Amphastar Pharmaceuticals, Inc.	$ 29,548	$ 3,919	$ 42,356	$ 7,676
Other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc., net of income taxes
Reclassification of adjustment for amounts included in net income	(362)		(362)
Foreign currency translation adjustment	(984)	695	(2,194)	209
Total other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.	(1,346)	695	(2,556)	209
Total comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.	$ 28,202	$ 4,614	$ 39,800	$ 7,885

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 income (loss) attributable to non-controlling interest							(424)	(424)
Purchase of treasury stock					$ (10,950)	(10,950)		(10,950)
Purchase of treasury stock (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, 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.								7,676
Other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.								209
Balance at Sep. 30, 2020	$ 5	404,084	124,046	(4,478)	$ (118,425)	405,232		450,962
Balance at Sep. 30, 2020							45,730
Balance at Sep. 30, 2020	54,623,837				(7,089,622)
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)
Changes in Stockholders' Equity
Net income (loss) attributable to Amphastar Pharmaceuticals, Inc.			(192)			(192)		(192)
Other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.				288		288		288
Net income (loss) attributable to non-controlling interest							(1,237)	(1,237)
Purchase of treasury stock					$ (5,756)	(5,756)		(5,756)
Purchase of treasury stock (in shares)					(329,391)
Issuance of treasury stock in connection with the Company's equity plans		(130)			$ 130
Issuance of treasury stock in connection with the Company's equity plans (in Shares)					10,913
Issuance of common stock in connection with the Company's equity plans		19,448				19,448		19,448
Issuance of common stock in connection with the Company's equity plans (in Shares)	1,507,284
Share-based compensation expense		6,379				6,379	134	6,513
Balance at Jun. 30, 2020	$ 5	396,841	120,127	(5,173)	$ (114,119)	397,681	44,756
Balance at Jun. 30, 2020								442,437
Balance at Jun. 30, 2020	54,372,275				(6,877,366)
Changes in Stockholders' Equity
Net income (loss) attributable to Amphastar Pharmaceuticals, Inc.			3,919			3,919		3,919
Other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.				695		695		695
ANP Restructuring							(106)	(106)
Net income (loss) attributable to non-controlling interest							874	874
Purchase of treasury stock					$ (4,329)	(4,329)		(4,329)
Purchase of treasury stock (in shares)					(214,256)
Issuance of treasury stock in connection with the Company's equity plans		(23)			$ 23
Issuance of treasury stock in connection with the Company's equity plans (in Shares)					2,000
Issuance of common stock in connection with the Company's equity plans		3,102				3,102		3,102
Issuance of common stock in connection with the Company's equity plans (in Shares)	251,562
Share-based compensation expense		4,164				4,164	206	4,370
Balance at Sep. 30, 2020	$ 5	404,084	124,046	(4,478)	$ (118,425)	405,232		450,962
Balance at Sep. 30, 2020							45,730
Balance at Sep. 30, 2020	54,623,837				(7,089,622)
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 income (loss) attributable to non-controlling interest							(1,082)	(1,082)
Purchase of treasury stock					$ (3,783)	(3,783)		(3,783)
Purchase of treasury stock (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
Balance at Mar. 31, 2021								450,960
Balance at Mar. 31, 2021	55,184,000				(7,465,997)
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.								$ 42,356
Other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.								(2,556)
Balance at Sep. 30, 2021	$ 6	412,917	160,577	(6,277)	$ (137,047)	430,176		430,176
Balance at Sep. 30, 2021								$ 430,176
Balance at Sep. 30, 2021	56,051,622				(8,068,972)			47,982,690
Balance at Mar. 31, 2021	$ 6	413,926	122,814	(5,642)	$ (125,546)	405,558	45,402
Balance at Mar. 31, 2021								$ 450,960
Balance at Mar. 31, 2021	55,184,000				(7,465,997)
Changes in Stockholders' Equity
Net income (loss) attributable to Amphastar Pharmaceuticals, Inc.			7,767			7,767		7,767
Other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.				711		711		711
Net income (loss) attributable to non-controlling interest							855	855
Purchase of treasury stock					$ (5,560)	(5,560)		(5,560)
Purchase of treasury stock (in shares)					(298,727)
Issuance of treasury stock in connection with the Company's equity plans		(142)			$ 142
Issuance of treasury stock in connection with the Company's equity plans (in Shares)					12,064
Issuance of common stock in connection with the Company's equity plans		7,247				7,247		7,247
Issuance of common stock in connection with the Company's equity plans (in Shares)	552,209
Share-based compensation expense		6,270				6,270	(1,027)	5,243
Balance at Jun. 30, 2021	$ 6	427,301	130,581	(4,931)	$ (130,964)	421,993	45,230
Balance at Jun. 30, 2021								467,223
Balance at Jun. 30, 2021	55,736,209				(7,752,660)
Changes in Stockholders' Equity
Net income (loss) attributable to Amphastar Pharmaceuticals, Inc.			29,548			29,548		29,548
Other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.								(1,346)
Other comprehensive income (loss) attributable to Amphastar Pharmaceuticals, Inc.				(984)		(984)		(984)
ANP Restructuring		(22,162)	448	(362)		(22,076)	(46,642)	(68,718)
Net income (loss) attributable to non-controlling interest							$ 1,412	1,412
Purchase of treasury stock					$ (6,094)	(6,094)		(6,094)
Purchase of treasury stock (in shares)					(317,212)
Issuance of treasury stock in connection with the Company's equity plans		(11)			$ 11
Issuance of treasury stock in connection with the Company's equity plans (in Shares)					900
Issuance of common stock in connection with the Company's equity plans		3,869				3,869		3,869
Issuance of common stock in connection with the Company's equity plans (in Shares)	315,413
Share-based compensation expense		3,920				3,920		3,920
Balance at Sep. 30, 2021	$ 6	$ 412,917	$ 160,577	$ (6,277)	$ (137,047)	$ 430,176		430,176
Balance at Sep. 30, 2021								$ 430,176
Balance at Sep. 30, 2021	56,051,622				(8,068,972)			47,982,690

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash Flows From Operating Activities:
Net income (loss)	$ 43,541	$ 6,889
Reconciliation to net cash provided by operating activities:
Loss (gain) on impairment and disposal of assets	338	161
Gain on deconsolidation of subsidiary	(13,587)
Depreciation of property, plant, and equipment	16,800	14,946
Amortization of product rights, trademarks, and patents	930	771
Operating lease right-of-use asset amortization	2,471	2,693
Share-based compensation	14,837	16,165
Changes in deferred taxes, net	5,170	3,638
Changes in operating assets and liabilities:
Accounts receivable, net	(14,166)	(6,706)
Inventories	(5,768)	2,351
Prepaid expenses and other assets	2,463	(3,755)
Income tax refunds, deposits, and payables, net	2,832	(1,973)
Operating lease liabilities	(2,529)	(2,478)
Accounts payable and accrued liabilities	4,221	7,671
Net cash provided by operating activities	57,553	40,373
Cash Flows From Investing Activities:
Purchases and construction of property, plant, and equipment	(20,578)	(24,526)
Purchase of short-term investments	(12,459)	(10,930)
Maturity of short-term investments	17,423	11,891
Payment of deposits and other assets	(1,104)	(674)
Net cash used in investing activities	(16,718)	(24,239)
Cash Flows From Financing Activities:
Acquisition of additional ownership interest in ANP		(106)
ANP restructuring (see Note 3)	(53,592)
Proceeds from equity plans, net of withholding tax payments	10,264	21,312
Purchase of treasury stock	(15,437)	(21,035)
Settlement of ANP equity awards	(839)
Debt issuance costs	(1,430)
Proceeds from borrowing under lines of credit		1,072
Repayments under lines of credit	(1,161)
Proceeds from issuance of long-term debt	70,000	3,067
Principal payments on long-term debt	(36,127)	(6,329)
Net cash provided by (used in) financing activities	(28,322)	(2,019)
Effect of exchange rate changes on cash	(175)	110
Net increase (decrease) in cash, cash equivalents and restricted cash	12,338	14,225
Cash, cash equivalents, and restricted cash at beginning of period	94,507	75,550
Cash, cash equivalents, and restricted cash at end of period	106,845	89,775
Noncash Investing and Financing Activities:
Capital expenditure included in accounts payable	6,246	6,477
Operating lease right-of-use assets	11,015	4,119
Equipment acquired under finance leases	107	61
Supplemental Disclosures of Cash Flow Information:
Interest paid, net of capitalized interest	1,868	1,678
Income taxes paid	$ 5,480	$ 2,807

General

General	9 Months Ended
	Sep. 30, 2021
General
General	Note 1. General ​ 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	9 Months Ended
	Sep. 30, 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. In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments, which are of a normal recurring nature, necessary to present fairly the consolidated financial position, results of operations, and cash flows of the Company. ​ The Company’s subsidiaries include: (1) International Medication Systems, Limited, or IMS, (2) Armstrong Pharmaceuticals, Inc., or Armstrong, (3) Amphastar Nanjing Pharmaceuticals Inc., or ANP, (4) Amphastar France Pharmaceuticals, S.A.S., or AFP, (5) Amphastar UK Ltd., or AUK, and (6) International Medication Systems (UK) Limited, or IMS UK. ​ 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-19 on the assumptions and estimates used to determine the results reported and asset valuations as of September 30, 2021. ​ 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. ​ Investments in Unconsolidated Affiliates ​ The Company applies the equity method of accounting for investments when it has significant influence, but not controlling interest in the investee. Judgment regarding the level of influence over each equity method investment includes key factors such as ownership interest, representation on the board of directors, participation in policy-making decisions and material intercompany transactions. The Company’s proportionate share of the earnings or losses resulting from these investments is reported as “Equity in earnings of unconsolidated affiliates” in the consolidated statements of operations. Investments accounted for using the equity method may be reported on a lag of up to three months if financial statements of the investee are not available in sufficient time for the investor to apply the equity method as of the current reporting date. The determination of whether an investee’s results are recorded on a lag is made on an investment-by-investment basis. ​ The carrying value of equity method investments is reported as “Equity method investments” in the consolidated balance sheets. The Company’s equity method investments are reported at cost and adjusted each period for the Company’s share of the investee’s earnings or losses and dividends paid, if any. ​ The Company assesses investments for impairment whenever events or changes in circumstances indicate that the carrying value of an investment may not be recoverable. If the decline in value is considered to be other than temporary, the investment is written down to its estimated fair value, which establishes a new cost basis in the investment. The Company did not record any such impairment charges for all periods presented. ​ 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, fair value of financial instruments, allowance for discounts, provision for chargebacks and rebates, provision for product returns, adjustment of inventory to its 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. 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 or losses on intercompany foreign currency transactions that are of a long-term investment nature were a $0.9 million loss and a $1.9 million loss for the three and nine months ended September 30, 2021, respectively. For the three and nine months ended September 30, 2020, the unrealized gains on intercompany foreign currency transactions that are of a long-term investment nature were a $1.4 million. ​ Comprehensive Income (Loss) ​ For the three and nine months ended September 30, 2021 and 2020, the Company included its foreign currency translation gain or loss as part of its comprehensive income (loss). There was no material income tax expense (benefit) allocated to other comprehensive income (loss) for the three and nine months ended September 30, 2021. Income tax expense of $0.4 million was allocated to other comprehensive income for both the three and nine months ended September 30, 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 September 30, 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 September 30, 2021 and December 31, 2020, the restricted cash balances were $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 September 30, 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 ​ There have been no recent accounting pronouncements or changes in accounting pronouncements during the three months ended September 30, 2021 that are of significance or potential significance to the Company as compared to the recent accounting pronouncements described in the Company’s Annual Report on Form 10-K filed with the SEC on March 15, 2021.

ANP Restructuring

ANP Restructuring	9 Months Ended
	Sep. 30, 2021
ANP Restructuring
ANP Restructuring	Note 3. ANP Restructuring ​ 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. The Company 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. ​ In May 2021, the Company’s Board of Directors approved a plan for the restructuring of the equity ownership of ANP, whereby the Company purchased an additional ownership interest in ANP from certain equity holders of ANP, or the Sellers, and split-off certain subsidiaries of ANP. Under the terms of the restructuring plan, the Company entered into a Share Purchase Agreement, or SPA, with certain of the Sellers to acquire an approximately 18% additional ownership interest in ANP for approximately $29.4 million in cash. The Company also entered into a Share Repurchase Agreement, or SRA, with certain of the Sellers, whereby the Company contributed 80% of its ownership interest in Hanxin and Hanxin’s existing subsidiaries, Baixin and Letop, to the Sellers in exchange for an approximately 10% additional ownership interest in ANP. Following completion of these transactions, the Company ownership increased to approximately 85% of the equity interest in ANP. ​ In August 2021, the Company entered into a second Share Purchase Agreement, or Second SPA, with the sole remaining equity holder of ANP to acquire the remaining approximately 15% of ownership interest in ANP. The total cash payment by the Company for this transaction was approximately $22.5 million. Following completion of the transaction, the Company’s ownership of ANP increased to 100%. ​ Certain of the Sellers are the Company’s executive officers, directors and other related parties. The Sellers who participated in the SPA included executives of the Company William J. Peters, Rong Zhou, and Jacob Liawatidewi; directors of the Company Howard Lee and Richard Koo; relatives of Dr. Jack Zhang and Dr. Mary Luo, Henry Zhang, Qingqing Chen, Chongqing Zhang, Lu Zhang, and James Luo, or entities related to such persons. ​ The Sellers who participated in the SRA included Dr. Mary Luo and Dr. Jack Zhang through an affiliated party, and their family members Henry Zhang, Qingqing Chen, Chongqing Zhang, Bill Zhang, and Lu Zhang. Sellers who participated in the Second SPA include Dr. Mary Luo, Dr. Jack Zhang, through an affiliated party, and their family members Chongqing Zhang and Bill Zhang. ​ The restructuring of ANP was completed in the third quarter of 2021. As a result of the restructuring activities, the Company’s ownership interest in ANP was increased to 100%, and ANP’s ownership interest in Hanxin and its subsidiaries was reduced to approximately 20%. ​ The reduction of the Company’s ownership in Hanxin to 20%, resulted in ANP experiencing a “loss of control” of a subsidiary as defined by GAAP. Loss of control is deemed to have occurred when, among other things, a parent company owns less than a majority of the outstanding common stock in the subsidiary, lacks a controlling financial interest in the subsidiary and, is unable to unilaterally control the subsidiary through other means such as having, or being able to obtain, the power to elect a majority of the subsidiary's board of directors based solely on contractual rights or ownership of shares holding a majority of the voting power of the subsidiary's voting securities. These loss-of-control factors were met with respect to ANP’s ownership interest in Hanxin after the restructuring. ​ Accordingly, on completion of the SRA in the third quarter, the Company deconsolidated Hanxin and recorded a $13.6 million gain on deconsolidation, which is recognized in other income (expenses), net, in the consolidated statement of operations for the three and nine months ended September 30, 2021. Of the $13.6 million gain recorded, approximately $2.7 million related to the remeasurement of the retained noncontrolling investment in Hanxin. The remainder of the gain relates to the excess of the fair value the consideration received, over the book value of Hanxin’s net assets. ​ Hanxin continues to be a related party after the deconsolidation. ​ In addition to the retained noncontrolling investment in Hanxin, the Company maintains a seat on Hanxin’s board of directors, and Henry Zhang, a relative of Dr. Jack Zhang and Dr. Mary Luo, is an equity holder, general manager, and chairman of the board of directors of Hanxin. As a result, it was determined that the Company has significant influence over Hanxin and as such the retained noncontrolling investment in Hanxin is accounted for as an equity method investment. ​ As an equity method investment, the retained noncontrolling 20% investment in Hanxin was recorded at fair value in the amount of $4.2 million, which exceeds the amount of underlying equity in Hanxin’s net assets by $2.7 million. This basis difference was deemed to be a premium in excess of fair value, which is referred to as equity method goodwill, and is recorded within the “Equity Method Investment” line on the Company’s consolidated balance sheets. The fair value of the noncontrolling investment in Hanxin was determined using a discounted cash flow model using Level 3 inputs. ​ Subsequent to the restructuring, during the third quarter of 2021, Hanxin received additional capital contributions resulting in further reduction of ANP’s ownership to approximately 14%. ​ During the second quarter of 2021, in connection with the restructuring, the Company terminated the 2018 ANP Equity Incentive Plan. (See note 16)

Revenue Recognition

Revenue Recognition	9 Months Ended
	Sep. 30, 2021
Revenue Recognition
Revenue Recognition	Note 4. 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: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended ​ ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 20,380 $ 21,644 ​ Provision for chargebacks and rebates ​ 151,174 ​ 110,763 ​ Credits and payments issued to third parties ​ (154,143) ​ (113,576) ​ Ending balance ​ $ 17,411 ​ $ 18,831 ​ ​ 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 September 30, 2021 and December 31, 2020, $13.5 million and $16.4 million were included in accounts receivable, net, on the condensed consolidated balance sheets, respectively. The remaining provision as of September 30, 2021 and December 31, 2020 of $3.9 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: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended ​ ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 14,204 $ 10,339 ​ Provision for product returns ​ 11,714 ​ 9,084 ​ Credits issued to third parties ​ (6,183) ​ (6,731) ​ Ending balance ​ $ 19,735 ​ $ 12,692 ​ ​ Of the provision for product returns as of September 30, 2021 and December 31, 2020, $14.8 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 September 30, 2021 and December 31, 2020, of $4.9 million and $4.0 million, were included in other long-term liabilities, respectively. For the nine months ended September 30, 2021 and 2020, the Company’s aggregate product return rate was 1.7% and 1.3% of qualified sales, respectively.

Income (Loss) per Share Attribu

Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders	9 Months Ended
	Sep. 30, 2021
Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders
Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders	Note 5. 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. ​ For the three and nine months ended September 30, 2021, options to purchase 1,885,093 and 2,045,878 shares of stock, respectively, with a weighted-average exercise price of $20.86 per share and $20.74 per share, respectively, were excluded from the computation of diluted net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders because the effect would be anti-dilutive. ​ For the three and nine months ended September 30, 2020, options to purchase 1,271,347 and 1,928,629 shares of stock, respectively, with a weighted-average exercise price of $21.35 per share and $20.84 per share, respectively, and the reallocation of net income attributable to non-controlling interests were excluded in the computation of diluted net income per common 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 ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ ​ (in thousands, except per share data) ​ Basic and dilutive numerator: ​ ​ ​ ​ Net income attributable to Amphastar Pharmaceuticals, Inc. ​ $ 29,548 ​ $ 3,919 ​ $ 42,356 ​ $ 7,676 ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average shares outstanding — basic ​ 48,022 ​ 47,496 ​ 47,758 ​ 46,886 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net effect of dilutive securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Incremental shares from equity awards ​ 1,987 ​ 2,352 ​ 1,935 ​ 2,036 ​ Weighted-average shares outstanding — diluted ​ 50,009 ​ 49,848 ​ 49,693 ​ 48,922 ​ Net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders — basic ​ $ 0.62 ​ $ 0.08 ​ $ 0.89 ​ $ 0.16 ​ Net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders — diluted ​ $ 0.59 ​ $ 0.08 ​ $ 0.85 ​ $ 0.16 ​ ​

Segment Reporting

Segment Reporting	9 Months Ended
	Sep. 30, 2021
Segment Reporting
Segment Reporting	Note 6. 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 ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Net revenues: ​ ​ ​ ​ Finished pharmaceutical products ​ $ 108,990 ​ $ 81,335 ​ $ 301,594 ​ $ 243,568 ​ API ​ 3,208 ​ ​ 2,096 ​ ​ 15,287 ​ ​ 10,357 ​ Total net revenues ​ 112,198 ​ 83,431 ​ 316,881 ​ 253,925 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross profit (loss): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Finished pharmaceutical products ​ 54,602 ​ 39,546 ​ 149,502 ​ 113,793 ​ API ​ (3,419) ​ ​ (3,038) ​ ​ (5,997) ​ ​ (7,285) ​ Total gross profit ​ 51,183 ​ 36,508 ​ 143,505 ​ 106,508 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating expenses ​ 26,414 ​ 32,991 ​ 97,870 ​ 98,433 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Income from operations ​ 24,769 ​ 3,517 ​ 45,635 ​ 8,075 ​ Non-operating income ​ 12,877 ​ 3,561 ​ 11,342 ​ 3,304 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Income before income taxes ​ $ 37,646 ​ $ 7,078 ​ $ 56,977 ​ $ 11,379 ​ ​ 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 ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Finished pharmaceutical products net revenues: ​ ​ ​ ​ ​ Primatene Mist ® ​ $ 16,561 ​ $ 12,988 ​ $ 51,624 ​ $ 38,333 ​ Epinephrine ​ ​ 13,892 ​ ​ 5,370 ​ ​ 38,662 ​ ​ 16,317 ​ Lidocaine ​ ​ 11,649 ​ ​ 10,657 ​ ​ 32,314 ​ ​ 28,922 ​ Glucagon ​ ​ 12,189 ​ ​ — ​ ​ 32,304 ​ ​ — ​ Phytonadione ​ 11,591 ​ 10,470 ​ 31,577 ​ 32,188 ​ Enoxaparin ​ ​ 8,034 ​ ​ 11,647 ​ ​ 28,020 ​ ​ 31,033 ​ Naloxone ​ ​ 8,028 ​ ​ 8,739 ​ ​ 20,994 ​ ​ 26,337 ​ Other finished pharmaceutical products ​ 27,046 ​ 21,464 ​ 66,099 ​ 70,438 ​ Total finished pharmaceutical products net revenues ​ $ 108,990 ​ $ 81,335 ​ $ 301,594 ​ $ 243,568 ​ ​ The amount of depreciation and amortization expense included in cost of revenues, by reporting segments, is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Depreciation and amortization expense ​ ​ ​ ​ Finished pharmaceutical products ​ $ 1,534 ​ $ 1,408 ​ $ 4,429 ​ $ 4,325 ​ API ​ 970 ​ 1,048 ​ 3,197 ​ ​ 2,205 ​ Total depreciation and amortization expense ​ $ 2,504 ​ $ 2,456 ​ $ 7,626 ​ $ 6,530 ​ ​ Net revenues and carrying values of long-lived assets by geographic regions are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net Revenue ​ Long-Lived Assets ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ September 30, ​ September 30, ​ December 31, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ (in thousands) United States $ 107,829 $ 79,407 $ 302,192 $ 242,370 $ 134,684 $ 129,401 ​ China ​ 2,554 ​ ​ 1,959 ​ ​ 4,801 ​ ​ 2,482 ​ 89,385 ​ 98,538 ​ France ​ 1,815 ​ ​ 2,065 ​ ​ 9,888 ​ ​ 9,073 ​ 46,946 ​ 52,770 ​ Total ​ $ 112,198 ​ $ 83,431 ​ $ 316,881 ​ $ 253,925 ​ $ 271,015 ​ $ 280,709 ​ ​

Customer and Supplier Concentra

Customer and Supplier Concentration	9 Months Ended
	Sep. 30, 2021
Customer and Supplier Concentration
Customer and Supplier Concentration	Note 7. 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 and nine months ended September 30, 2021 and 2020, and accounts receivable as of September 30, 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 ​ Nine Months Ended ​ ​ September 30, ​ December 31, ​ September 30, ​ September 30, ​ ​ 2021 2020 2021 2020 2021 2020 AmerisourceBergen 15 % 9 % 25 % 23 % 24 % 23 % McKesson 23 % 24 % 21 % 21 % 20 % 22 % Cardinal Health 20 % 17 % 18 % 17 % 16 % 18 % ​ 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	9 Months Ended
	Sep. 30, 2021
Fair Value Measurements
Fair Value Measurements	Note 8. 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 September 30, 2021, cash equivalents include money market accounts. Short-term investments consist of certificates of deposit as well as investment-grade 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 September 30, 2021 and December 31, 2020, are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total (Level 1) (Level 2) (Level 3) ​ ​ (in thousands) Cash equivalents - money market ​ $ 82,146 ​ $ 82,146 ​ $ — ​ $ — ​ Restricted cash - money market ​ ​ 235 ​ ​ 235 ​ ​ — ​ ​ — ​ Short-term investments - certificates of deposit ​ ​ 5,102 ​ ​ — ​ ​ 5,102 ​ ​ — ​ Restricted short-term investments - certificates of deposit ​ 2,200 ​ — ​ 2,200 ​ — ​ Corporate and municipal bonds ​ ​ 3,039 ​ ​ — ​ ​ 3,039 ​ ​ — ​ Interest rate swap liabilities related to variable rate loans ​ ​ (279) ​ ​ — ​ ​ (279) ​ ​ — ​ Fair value measurement as of September 30, 2021 ​ $ 92,443 ​ $ 82,381 ​ $ 10,062 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 investments in unconsolidated affiliates, long-lived assets, goodwill, and intangible assets for which the fair value is determined as part of the related impairment test. As of September 30, 2021, and December 31, 2020, there were no significant adjustments to fair value for nonfinancial assets or liabilities.

Investments

Investments	9 Months Ended
	Sep. 30, 2021
Investments
Investments	Note 9. 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 ​ $ 513 ​ $ — ​ $ (1) ​ $ 512 Municipal bonds ​ ​ 2,527 ​ ​ — ​ ​ — ​ ​ 2,527 Total investments as of September 30, 2021 ​ $ 3,040 ​ $ — ​ $ (1) ​ $ 3,039 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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. ​ Investment in Hanxin ​ As a result of the ANP restructuring that was completed during the third quarter of 2021 (see Note 3), the Company has a 14% noncontrolling investment in Hanxin that is accounted for as an equity method investment. ​ The Company accounts for its share of the earnings or losses of Hanxin with a reporting lag of three months, as the financial statements of Hanxin are not completed on a basis that is sufficient for the Company to apply the equity method on a current basis. Hanxin became an equity method investment during the third quarter of 2021, and as such, no shares of earnings or losses of Hanxin were recorded in the condensed consolidated statement of operations for the three and nine months ended September 30, 2021. ​ ​

Goodwill and Intangible Assets

Goodwill and Intangible Assets	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets
Goodwill and Intangible Assets	Note 10. 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 ​ $ 9,416 ​ $ 4,865 ​ $ 4,551 ​ Patents 12 ​ 486 ​ ​ 329 ​ 157 ​ Land-use rights 39 ​ 2,540 ​ ​ 667 ​ 1,873 ​ Subtotal 12 ​ 12,442 ​ 5,861 ​ 6,581 ​ Indefinite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Trademark * ​ 29,225 ​ — ​ 29,225 ​ Goodwill - Finished pharmaceutical products * ​ 3,386 ​ — ​ 3,386 ​ Subtotal * ​ 32,611 ​ — ​ 32,611 ​ As of September 30, 2021 * ​ $ 45,053 ​ $ 5,861 ​ $ 39,192 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 3,940 $ 3,634 ​ ANP restructuring ​ ​ (374) ​ ​ — ​ Currency translation ​ (180) ​ 306 ​ Ending balance ​ $ 3,386 ​ $ 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	9 Months Ended
	Sep. 30, 2021
Inventories
Inventories	Note 11. Inventories ​ Inventories consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Raw materials and supplies $ 45,752 $ 47,051 ​ Work in process ​ 37,555 ​ 37,257 ​ Finished goods ​ 16,933 ​ 12,523 ​ Total inventories ​ $ 100,240 ​ $ 96,831 ​ ​ ​ ​ Charges of $6.1 million and $17.0 million were included in the cost of revenues in the Company’s condensed consolidated statements of operations for the three and nine months ended September 30, 2021, respectively, to adjust the Company’s inventory and related firm purchase commitments to their net realizable value. For the three and nine months ended September 30, 2020, charges of $2.5 million and $12.7 million were included in the cost of revenues, 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 $3.5 million and $4.2 million as of September 30, 2021 and 2020, respectively.

Property, Plant, and Equipment

Property, Plant, and Equipment	9 Months Ended
	Sep. 30, 2021
Property, Plant, and Equipment
Property, Plant, and Equipment	Note 12. Property, Plant, and Equipment ​ Property, plant, and equipment consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Buildings $ 127,700 $ 124,326 ​ Leasehold improvements ​ 27,356 ​ 30,028 ​ Land ​ 7,645 ​ 7,719 ​ Machinery and equipment ​ 207,595 ​ 211,666 ​ Furniture, fixtures, and automobiles ​ 27,123 ​ 26,482 ​ Construction in progress ​ 40,057 ​ 43,981 ​ Total property, plant, and equipment ​ 437,476 ​ 444,202 ​ Less accumulated depreciation ​ (194,552) ​ (184,147) ​ Total property, plant, and equipment, net ​ $ 242,924 ​ $ 260,055 ​ ​

Accounts Payable and Accrued Li

Accounts Payable and Accrued Liabilities	9 Months Ended
	Sep. 30, 2021
Accounts Payable and Accrued Liabilities.
Accounts Payable and Accrued Liabilities	Note 13. Accounts Payable and Accrued Liabilities ​ Accounts payable and accrued liabilities consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ 2021 ​ 2020 ​ (in thousands) Accrued customer fees and rebates $ 11,581 ​ $ 9,029 Accrued payroll and related benefits ​ 27,324 ​ ​ 24,597 Accrued product returns, current portion ​ 14,823 ​ ​ 10,190 Accrued loss on firm purchase commitments ​ 3,449 ​ ​ 1,223 Accrued litigation and settlements ​ — ​ ​ 13,780 Other accrued liabilities ​ 10,076 ​ ​ 12,328 Total accrued liabilities 67,253 ​ 71,147 Accounts payable 21,658 ​ 24,357 Total accounts payable and accrued liabilities $ 88,911 ​ $ 95,504 ​

Debt

Debt	9 Months Ended
	Sep. 30, 2021
Debt
Debt	Note 14. Debt ​ Debt consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Line of Credit Facilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Line of credit facility with China Everbright Bank - closed June 2021 ​ $ — ​ $ 764 ​ Line of credit facility with China Merchant Bank ​ ​ — ​ ​ 382 ​ Line of credit facility with Bank of Nanjing - deconsolidated (see Note 3) ​ ​ — ​ ​ 153 ​ Line of credit facility with Cathay Bank - closed in August 2021 ​ — ​ — ​ Line of credit facility with East West Bank - closed in August 2021 ​ ​ — ​ ​ — ​ Equipment line of credit facility with East West Bank - closed in August 2021 ​ ​ — ​ ​ 3,216 ​ Revolving line of credit facility with Capital One N.A. due August 2026 ​ ​ — ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ Term Loan ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Term loan with Capital One N.A. due August 2026 ​ ​ 70,000 ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ Mortgage Loans ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mortgage payable with East West Bank paid off May 2021 ​ ​ — ​ ​ 3,306 ​ Mortgage payable with East West Bank paid off August 2021 ​ ​ — ​ ​ 3,334 ​ Mortgage payable with Cathay Bank paid off August 2021 ​ — ​ 7,268 ​ Mortgage payable with East West Bank due June 2027 ​ ​ 8,393 ​ ​ 8,510 ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment Loans ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment loan with East West Bank paid off June 2021 ​ ​ — ​ ​ 612 ​ Equipment loan with East West Bank paid off August 2021 ​ ​ — ​ ​ 4,000 ​ Equipment loan with East West Bank paid off August 2021 ​ ​ — ​ ​ 5,254 ​ ​ ​ ​ ​ ​ ​ ​ ​ Other Loans and Payment Obligations ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Acquisition loan with Cathay Bank paid off August 2021 ​ — ​ 8,710 ​ French government loan paid off July 2021 ​ ​ — ​ ​ 64 ​ French government loans due December 2026 ​ ​ 339 ​ ​ 350 ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment under Finance Leases ​ 471 ​ 526 ​ Total debt ​ 79,203 ​ 46,449 ​ Less current portion of long-term debt ​ 2,256 ​ 12,263 ​ Less: Loan issuance costs ​ ​ 1,395 ​ ​ 84 ​ Long-term debt, net of current portion and unamortized debt issuance costs ​ $ 75,552 ​ $ 34,186 ​ ​ As of September 30, 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 the mortgage loan with East West Bank, the Company has entered into fixed interest rate swap contracts to exchange the variable interest rate for a fixed interest rate over the life of the debt instrument without the exchange of the underlying notional debt amount. ​ Credit Agreement with Capital One N.A. - Due August 2026 ​ In August 2021, the Company entered into a $140.0 million credit agreement with Capital One N.A. acting as a lender and as agent for other lenders. Under the terms of the credit agreement, the Company borrowed $70.0 million in the form of a term loan. Proceeds from the loan were used to pay down certain of the Company’s outstanding loans and revolving lines of credit with Cathay Bank and East West Bank. The interest rate on the term loan is based on a variable interest rate, plus an applicable margin rate ranging between 0.5% and 2.5%, determined based on the Company’s net leverage ratio as defined by the terms of the agreement. The loan matures in August 2026. ​ At September 30, 2021, the interest rate on this loan was 1.84%. ​ The loan requires principal payments of $1.8 million per year for the first two years, which increases to $3.5 million during the third and fourth year and to $3.9 million in the fifth year, with the remaining balance due at maturity. The loan is secured by substantially all of the Company’s assets, excluding the assets of ANP. ​ The credit agreement provides for a $70.0 million revolving credit facility, which bears a variable interest rate, plus a fixed margin. ​ In conjunction with the new credit agreement, the Company entered into an interest rate swap agreement with Capital One N.A., with a notional amount of $55.0 million to exchange the variable interest rate on the new term loan for a fixed rate of 0.93%. ​ The Company incurred approximately $1.4 million in issuance costs in connection with this credit agreement, which is being amortized over the term of the loan.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Taxes
Income Taxes	Note 15. Income Taxes ​ The following table sets forth the Company’s income tax provision for the periods indicated: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2021 2020 2021 2020 ​ ​ (in thousands) Income before taxes ​ $ 37,646 ​ $ 7,078 ​ $ 56,977 ​ $ 11,379 ​ Income tax provision ​ ​ 6,686 ​ 2,285 ​ ​ 13,436 ​ 4,490 ​ Net income ​ $ 30,960 ​ $ 4,793 ​ $ 43,541 ​ $ 6,889 ​ Income tax provision as a percentage of income before income taxes ​ ​ 17.8 % 32.3 % ​ 23.6 % 39.5 % ​ The change in the Company’s effective tax rate for the three and nine months ended September 30, 2021, was 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 subsidiary AFP and will continue to do so until AFP generates sufficient taxable income to realize its 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 $0.3 million for the three and nine months ended September 30, 2021, respectively. The increase in the Company’s income tax provision for the three and nine months ended September 30, 2020 was $0.2 million and $0.4 million, respectively.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity
Stockholders' Equity	Note 16. Stockholders' Equity ​ Share Buyback Program ​ Pursuant to the Company’s existing share buyback program, the Company purchased 317,212 and 820,637 shares of its common stock during the three and nine months ended September 30, 2021, for total consideration of $6.1 million and $15.4 million, respectively. The Company purchased 214,256 and 1,190,362 shares of its common stock during the three and nine months ended September 30, 2020, for total consideration of $4.3 million and $21.0 million, respectively. ​ In August 2021, 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. Since the inception of the program, the Company’s Board of Directors have authorized a total of $160.0 million to the Company’s share buyback program. 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 September 30, 2021, the Company reserved an aggregate of 5,997,738 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 September 30, 2021, the Company has issued 890,904 shares of common stock under the ESPP, and 1,109,096 shares of its common stock remains available for issuance under the ESPP. ​ In May 2021, the Company issued 83,354 shares at a weighted-average purchase price of $15.25 per share under the ESPP. For the three and nine months ended September 30, 2021, the Company recorded ESPP expense of $0.2 million and $0.5 million, respectively. For the three and nine months ended September 30, 2020, the Company recorded ESPP expense of $0.1 million and $0.5 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 and nine months ended September 30, 2021 and 2020, are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ Average volatility 41.4 % 43.7 % 42.1 % 43.1 % ​ Average risk-free interest rate 1.1 % 0.5 % 1.2 % 0.8 % ​ Weighted-average expected life in years 6.3 ​ 6.3 ​ 6.1 ​ 5.7 ​ ​ Dividend yield rate — % — % — % — % ​ ​ A summary of option activity for the nine months ended September 30, 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 1,436,929 ​ ​ 18.25 ​ ​ ​ ​ ​ ​ Options exercised (899,436) ​ ​ 13.49 ​ ​ ​ ​ ​ ​ Options cancelled (155,784) ​ ​ 17.02 ​ ​ ​ ​ ​ ​ Options expired (56,826) ​ ​ 14.67 ​ ​ ​ ​ ​ ​ Outstanding as of September 30, 2021 8,905,358 ​ $ 15.65 ​ 5.34 ​ $ 33,500 ​ Exercisable as of September 30, 2021 6,021,669 ​ $ 15.11 ​ 3.90 ​ $ 26,145 ​ (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 September 30, 2021. ​ For the three and nine months ended September 30, 2021, the Company recorded an expense of $1.9 million and $6.2 million, respectively, related to stock options granted. For the three and nine months ended September 30, 2020, the Company recorded an expense of $1.9 million and $7.1 million, respectively, related to stock options granted under all plans. ​ In April 2020, Jason Shandell resigned from his position as the Company’s President and General Counsel and as a member of the Company’s Board of Directors. In connection with his resignation, the Company and Mr. Shandell entered into a separation agreement. As part of the separation agreement, the Company agreed to accelerate 80% of his unvested stock options and extended the expiration date of certain vested stock option awards. As a result of this modification, the Company incurred share-based compensation expense of $0.7 million, which is included within general and administration expenses in the condensed consolidated statement of operations for the nine months ended September 30, 2020. Information relating to option grants and exercises is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands, except per share data) Weighted-average grant date fair value per option share ​ $ 8.00 ​ $ 8.64 ​ $ 7.62 ​ $ 5.50 ​ Intrinsic value of options exercised ​ 2,176 ​ 1,687 ​ 5,292 ​ 8,661 ​ Cash received from options exercised ​ 3,953 ​ 3,195 ​ 12,122 ​ 23,534 ​ Total fair value of the options vested during the period ​ 112 ​ 121 ​ 8,162 ​ 9,965 ​ ​ A summary of the status of the Company’s non-vested options as of September 30, 2021, and changes during the nine months ended September 30, 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 1,436,929 ​ 7.62 ​ Options vested (1,223,108) ​ 6.67 ​ Options forfeited (155,784) ​ 6.98 ​ Non-vested as of September 30, 2021 2,883,689 ​ 6.96 ​ ​ As of September 30, 2021, there was $14.1 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 2.6 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 and nine months ended September 30, 2021, the Company recorded total expenses of $1.9 million and $6.2 million, respectively, related to RSU awards granted. During the three and nine months ended September 30, 2020, the Company recorded expenses of $2.0 million and $8.0 million, respectively, related to RSU awards granted. ​ As part of the separation agreement with Mr. Shandell, the Company agreed to accelerate the vesting of 80% of his RSU awards. As a result of this modification, the Company incurred share-based compensation expense of $1.6 million, which is included within general and administrative expenses in the condensed consolidated statement of operations for the nine months ended September 30, 2020. ​ As of September 30, 2021, there was $15.0 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 2.6 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 600,207 ​ $ 10,941 ​ RSUs forfeited (64,030) ​ ​ ​ ​ RSUs vested (2) (493,007) ​ ​ ​ ​ RSUs outstanding at September 30, 2021 1,199,688 ​ ​ ​ ​ (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, 167,034 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 ANP Equity Incentive Plan, or the 2018 Plan, which was set to expire in December 2023. The 2018 Plan permitted the grant of stock options and other equity awards in ANP shares to ANP employees. ​ During the second quarter of 2021, in connection with the ANP restructuring, the 2018 Plan was terminated. ​ At the time of the 2018 Plan termination, the number of stock options outstanding was 5,018,880. As part of the termination, ANP cash settled 4,091,080 stock options, of which, 1,944,771 stock options were vested and 2,146,309 stock options were unvested, for $0.8 million which approximated the fair value of these awards at the time of settlement. The cash settlement of these awards was recorded as a reduction in equity. ​ For the remaining 927,800 stock option awards that were outstanding under the 2018 Plan, of which 56,925 stock options were vested and 870,875 were unvested, the Company cancelled these awards and issued replacement awards under the 2015 Plan. The modified awards vest over periods ranging from 1 to 2 years and have a 10-year contractual term. The cancellation and replacement of the awards was accounted for as a modification in accordance with ASC 718. ​ As a result of the modification, the Company incurred $2.3 million of share-based compensation expense, of which $1.8 million was recorded within general and administrative expenses in the condensed consolidated statement of operations for the nine months ended September 30, 2021, and the remaining $0.5 million which will be recognized over the vesting period of the modified awards. ​ Prior to the termination of the 2018 Plan, during the three and nine months ended September 30, 2020, the Company recorded expense of $0.2 million and $0.5 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 ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ 2021 2020 ​ ​ (in thousands) Cost of revenues $ 889 $ 947 $ 2,967 $ 3,276 ​ Operating expenses: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Selling, distribution, and marketing ​ 164 ​ 120 ​ 438 ​ 350 ​ General and administrative ​ 2,533 ​ 2,899 ​ 10,069 ​ 11,170 ​ Research and development ​ 333 ​ 404 ​ 1,363 ​ 1,369 ​ Total share-based compensation ​ $ 3,919 ​ $ 4,370 ​ $ 14,837 ​ $ 16,165 ​ ​

Employee Benefits

Employee Benefits	9 Months Ended
	Sep. 30, 2021
Employee Benefits
Employee Benefits	Note 17. 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 and nine months ended September 30, 2021 were approximately $0.5 million and $1.5 million, respectively, compared to the prior year expense of $0.4 million and $1.4 million for the three and nine months ended September 30, 2020, 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 0.3% as of September 30, 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 at September 30, 2021 and December 31, 2020. The Company recorded an immaterial amount of expense under the plan for the three and nine months ended September 30, 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. The plan assets were valued at approximately $2.7 million as of September 30, 2021. The plan liabilities were valued at approximately $2.7 million as of September 30, 2021. 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	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies
Commitments and Contingencies	Note 18. Commitments and Contingencies ​ Purchase Commitments ​ As of September 30, 2021, the Company has entered into commitments to purchase equipment and raw materials for an aggregate amount of approximately $56.2 million. The Company anticipates that most of these commitments with a remaining term in excess of one year will be fulfilled by 2022.

Related-Party Transactions

Related-Party Transactions	9 Months Ended
	Sep. 30, 2021
Related-Party Transactions
Related-Party Transactions	Note 19. Related Party Transactions ​ Subsequent to the ANP restructuring discussed in Note 3, which involved various related parties, Hanxin is no longer a wholly-owned subsidiary of the Company and was deconsolidated in the third quarter of 2021. ​ The Company determined that it has significant influence over Hanxin as a result of its 14% ownership interest, its seat on Hanxin’s board of directors, and Henry Zhang’s position as an equity holder, general manager, and chairman of the board of directors of Hanxin, given he is the son of Dr. Jack Zhang. Additionally, Dr. Mary Luo and Dr. Jack Zhang, through an affiliated entity, have an ownership interest in Hanxin and as such Hanxin continues to be a related party after the restructuring. ​ As of September 30, 2021, the Company had a receivable from Hanxin of approximately $2.5 million, the majority of which was collected subsequent to the end of the quarter.

Litigation

Litigation	9 Months Ended
	Sep. 30, 2021
Litigation
Litigation	Note 20. Litigation ​ Amphastar Pharmaceuticals, Inc. v. Aventis Pharma, SA ​ In January 2009, the Company filed a qui tam complaint in the U.S. District Court for the Central District of California, alleging that Aventis Pharma S.A., or Aventis, through its acquisition of a patent through false and misleading statements to the U.S. Patent and Trademark Office, as well as through false and misleading statements to the FDA, overcharged the federal and state governments for its Lovenox ® ​ 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, and on November 13, 2020, the Court issued an Order (“November Order”) awarding Aventis $12.1 million in attorneys’ fees and $0.7 million in cost and expenses. The Company recorded $12.8 million in other income (expenses), in the consolidated statement of operations for the year ended December 31, 2020. ​ 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 amount awarded to Aventis to $17.2 million. ​ On June 30, 2021, the Company and Aventis entered into a settlement agreement to settle the attorney fees’ and expenses claim for $14.5 million. The additional $1.7 million was recorded in other income (expenses), in the condensed consolidated statement of operations. The settlement was paid in full in the third quarter of 2021. ​ 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 January 2022. The Company’s 30-month FDA stay expires August 10, 2022. Currently, this lawsuit does not expose the Company to any liabilities, as the product has not been launched. The Company intends to vigorously defend this patent lawsuit. ​ 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. The Company accrued the amount of $1.0 million for this litigation as of March 31, 2021. On April 5, 2021, the parties reached a settlement for $1.0 million. On June 9, 2021, Ramirez submitted a motion to the Court to approve the settlement. On August 16, 2021, the Court approved Ramirez’s motion to approve the settlement. On September 13, 2021, consistent with the terms of the settlement agreement, the Company remitted payment for this case, thus resolving the matter. ​ 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.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 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. In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments, which are of a normal recurring nature, necessary to present fairly the consolidated financial position, results of operations, and cash flows of the Company. ​ The Company’s subsidiaries include: (1) International Medication Systems, Limited, or IMS, (2) Armstrong Pharmaceuticals, Inc., or Armstrong, (3) Amphastar Nanjing Pharmaceuticals Inc., or ANP, (4) Amphastar France Pharmaceuticals, S.A.S., or AFP, (5) Amphastar UK Ltd., or AUK, and (6) International Medication Systems (UK) Limited, or IMS UK. ​
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-19 on the assumptions and estimates used to determine the results reported and asset valuations as of September 30, 2021. ​ 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, fair value of financial instruments, allowance for discounts, provision for chargebacks and rebates, provision for product returns, adjustment of inventory to its 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.
Investments in Unconsolidated Affiliates	Investments in Unconsolidated Affiliates ​ The Company applies the equity method of accounting for investments when it has significant influence, but not controlling interest in the investee. Judgment regarding the level of influence over each equity method investment includes key factors such as ownership interest, representation on the board of directors, participation in policy-making decisions and material intercompany transactions. The Company’s proportionate share of the earnings or losses resulting from these investments is reported as “Equity in earnings of unconsolidated affiliates” in the consolidated statements of operations. Investments accounted for using the equity method may be reported on a lag of up to three months if financial statements of the investee are not available in sufficient time for the investor to apply the equity method as of the current reporting date. The determination of whether an investee’s results are recorded on a lag is made on an investment-by-investment basis. ​ The carrying value of equity method investments is reported as “Equity method investments” in the consolidated balance sheets. The Company’s equity method investments are reported at cost and adjusted each period for the Company’s share of the investee’s earnings or losses and dividends paid, if any. ​ The Company assesses investments for impairment whenever events or changes in circumstances indicate that the carrying value of an investment may not be recoverable. If the decline in value is considered to be other than temporary, the investment is written down to its estimated fair value, which establishes a new cost basis in the investment. The Company did not record any such impairment charges for all periods presented.
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. 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 or losses on intercompany foreign currency transactions that are of a long-term investment nature were a $0.9 million loss and a $1.9 million loss for the three and nine months ended September 30, 2021, respectively. For the three and nine months ended September 30, 2020, the unrealized gains on intercompany foreign currency transactions that are of a long-term investment nature were a $1.4 million. ​
Comprehensive Income (Loss)	Comprehensive Income (Loss) ​ For the three and nine months ended September 30, 2021 and 2020, the Company included its foreign currency translation gain or loss as part of its comprehensive income (loss). There was no material income tax expense (benefit) allocated to other comprehensive income (loss) for the three and nine months ended September 30, 2021. Income tax expense of $0.4 million was allocated to other comprehensive income for both the three and nine months ended September 30, 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 September 30, 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 September 30, 2021 and December 31, 2020, the restricted cash balances were $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 September 30, 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 ​ There have been no recent accounting pronouncements or changes in accounting pronouncements during the three months ended September 30, 2021 that are of significance or potential significance to the Company as compared to the recent accounting pronouncements described in the Company’s Annual Report on Form 10-K filed with the SEC on March 15, 2021.

Revenue Recognition (Tables)

Revenue Recognition (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue Recognition
Schedule of chargeback and rebates provision analysis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended ​ ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 20,380 $ 21,644 ​ Provision for chargebacks and rebates ​ 151,174 ​ 110,763 ​ Credits and payments issued to third parties ​ (154,143) ​ (113,576) ​ Ending balance ​ $ 17,411 ​ $ 18,831 ​
Schedule of product return liability analysis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended ​ ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 14,204 $ 10,339 ​ Provision for product returns ​ 11,714 ​ 9,084 ​ Credits issued to third parties ​ (6,183) ​ (6,731) ​ Ending balance ​ $ 19,735 ​ $ 12,692 ​

Income (Loss) per Share Attri_2

Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders (Tables)	9 Months Ended
	Sep. 30, 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 ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ ​ (in thousands, except per share data) ​ Basic and dilutive numerator: ​ ​ ​ ​ Net income attributable to Amphastar Pharmaceuticals, Inc. ​ $ 29,548 ​ $ 3,919 ​ $ 42,356 ​ $ 7,676 ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average shares outstanding — basic ​ 48,022 ​ 47,496 ​ 47,758 ​ 46,886 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net effect of dilutive securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Incremental shares from equity awards ​ 1,987 ​ 2,352 ​ 1,935 ​ 2,036 ​ Weighted-average shares outstanding — diluted ​ 50,009 ​ 49,848 ​ 49,693 ​ 48,922 ​ Net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders — basic ​ $ 0.62 ​ $ 0.08 ​ $ 0.89 ​ $ 0.16 ​ Net income per share attributable to Amphastar Pharmaceuticals, Inc. stockholders — diluted ​ $ 0.59 ​ $ 0.08 ​ $ 0.85 ​ $ 0.16 ​

Segment Reporting (Tables)

Segment Reporting (Tables)	9 Months Ended
	Sep. 30, 2021
Segment Reporting
Schedule of financial information by reporting segment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Net revenues: ​ ​ ​ ​ Finished pharmaceutical products ​ $ 108,990 ​ $ 81,335 ​ $ 301,594 ​ $ 243,568 ​ API ​ 3,208 ​ ​ 2,096 ​ ​ 15,287 ​ ​ 10,357 ​ Total net revenues ​ 112,198 ​ 83,431 ​ 316,881 ​ 253,925 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross profit (loss): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Finished pharmaceutical products ​ 54,602 ​ 39,546 ​ 149,502 ​ 113,793 ​ API ​ (3,419) ​ ​ (3,038) ​ ​ (5,997) ​ ​ (7,285) ​ Total gross profit ​ 51,183 ​ 36,508 ​ 143,505 ​ 106,508 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating expenses ​ 26,414 ​ 32,991 ​ 97,870 ​ 98,433 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Income from operations ​ 24,769 ​ 3,517 ​ 45,635 ​ 8,075 ​ Non-operating income ​ 12,877 ​ 3,561 ​ 11,342 ​ 3,304 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Income before income taxes ​ $ 37,646 ​ $ 7,078 ​ $ 56,977 ​ $ 11,379 ​
Schedule of net revenues in the finished pharmaceutical products segment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Finished pharmaceutical products net revenues: ​ ​ ​ ​ ​ Primatene Mist ® ​ $ 16,561 ​ $ 12,988 ​ $ 51,624 ​ $ 38,333 ​ Epinephrine ​ ​ 13,892 ​ ​ 5,370 ​ ​ 38,662 ​ ​ 16,317 ​ Lidocaine ​ ​ 11,649 ​ ​ 10,657 ​ ​ 32,314 ​ ​ 28,922 ​ Glucagon ​ ​ 12,189 ​ ​ — ​ ​ 32,304 ​ ​ — ​ Phytonadione ​ 11,591 ​ 10,470 ​ 31,577 ​ 32,188 ​ Enoxaparin ​ ​ 8,034 ​ ​ 11,647 ​ ​ 28,020 ​ ​ 31,033 ​ Naloxone ​ ​ 8,028 ​ ​ 8,739 ​ ​ 20,994 ​ ​ 26,337 ​ Other finished pharmaceutical products ​ 27,046 ​ 21,464 ​ 66,099 ​ 70,438 ​ Total finished pharmaceutical products net revenues ​ $ 108,990 ​ $ 81,335 ​ $ 301,594 ​ $ 243,568 ​
Schedule of depreciation and amortization expense by reporting segment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ ​ (in thousands) ​ Depreciation and amortization expense ​ ​ ​ ​ Finished pharmaceutical products ​ $ 1,534 ​ $ 1,408 ​ $ 4,429 ​ $ 4,325 ​ API ​ 970 ​ 1,048 ​ 3,197 ​ ​ 2,205 ​ Total depreciation and amortization expense ​ $ 2,504 ​ $ 2,456 ​ $ 7,626 ​ $ 6,530 ​
Schedule of net revenues and carrying values of long-lived assets by geographic region	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net Revenue ​ Long-Lived Assets ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ September 30, ​ September 30, ​ December 31, ​ ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ 2021 ​ 2020 ​ ​ (in thousands) United States $ 107,829 $ 79,407 $ 302,192 $ 242,370 $ 134,684 $ 129,401 ​ China ​ 2,554 ​ ​ 1,959 ​ ​ 4,801 ​ ​ 2,482 ​ 89,385 ​ 98,538 ​ France ​ 1,815 ​ ​ 2,065 ​ ​ 9,888 ​ ​ 9,073 ​ 46,946 ​ 52,770 ​ Total ​ $ 112,198 ​ $ 83,431 ​ $ 316,881 ​ $ 253,925 ​ $ 271,015 ​ $ 280,709 ​

Customer and Supplier Concent_2

Customer and Supplier Concentration (Tables)	9 Months Ended
	Sep. 30, 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 ​ Nine Months Ended ​ ​ September 30, ​ December 31, ​ September 30, ​ September 30, ​ ​ 2021 2020 2021 2020 2021 2020 AmerisourceBergen 15 % 9 % 25 % 23 % 24 % 23 % McKesson 23 % 24 % 21 % 21 % 20 % 22 % Cardinal Health 20 % 17 % 18 % 17 % 16 % 18 %

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 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 ​ $ 82,146 ​ $ 82,146 ​ $ — ​ $ — ​ Restricted cash - money market ​ ​ 235 ​ ​ 235 ​ ​ — ​ ​ — ​ Short-term investments - certificates of deposit ​ ​ 5,102 ​ ​ — ​ ​ 5,102 ​ ​ — ​ Restricted short-term investments - certificates of deposit ​ 2,200 ​ — ​ 2,200 ​ — ​ Corporate and municipal bonds ​ ​ 3,039 ​ ​ — ​ ​ 3,039 ​ ​ — ​ Interest rate swap liabilities related to variable rate loans ​ ​ (279) ​ ​ — ​ ​ (279) ​ ​ — ​ Fair value measurement as of September 30, 2021 ​ $ 92,443 ​ $ 82,381 ​ $ 10,062 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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)	9 Months Ended
	Sep. 30, 2021
Investments
Schedule of securities classified as held-to-maturity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) Corporate bonds ​ $ 513 ​ $ — ​ $ (1) ​ $ 512 Municipal bonds ​ ​ 2,527 ​ ​ — ​ ​ — ​ ​ 2,527 Total investments as of September 30, 2021 ​ $ 3,040 ​ $ — ​ $ (1) ​ $ 3,039 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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)	9 Months Ended
	Sep. 30, 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 ​ $ 9,416 ​ $ 4,865 ​ $ 4,551 ​ Patents 12 ​ 486 ​ ​ 329 ​ 157 ​ Land-use rights 39 ​ 2,540 ​ ​ 667 ​ 1,873 ​ Subtotal 12 ​ 12,442 ​ 5,861 ​ 6,581 ​ Indefinite-lived intangible assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Trademark * ​ 29,225 ​ — ​ 29,225 ​ Goodwill - Finished pharmaceutical products * ​ 3,386 ​ — ​ 3,386 ​ Subtotal * ​ 32,611 ​ — ​ 32,611 ​ As of September 30, 2021 * ​ $ 45,053 ​ $ 5,861 ​ $ 39,192 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Beginning balance $ 3,940 $ 3,634 ​ ANP restructuring ​ ​ (374) ​ ​ — ​ Currency translation ​ (180) ​ 306 ​ Ending balance ​ $ 3,386 ​ $ 3,940 ​

Inventories (Tables)

Inventories (Tables)	9 Months Ended
	Sep. 30, 2021
Inventories
Schedule of inventories	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Raw materials and supplies $ 45,752 $ 47,051 ​ Work in process ​ 37,555 ​ 37,257 ​ Finished goods ​ 16,933 ​ 12,523 ​ Total inventories ​ $ 100,240 ​ $ 96,831 ​

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant, and Equipment
Schedule of property, plant, and equipment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Buildings $ 127,700 $ 124,326 ​ Leasehold improvements ​ 27,356 ​ 30,028 ​ Land ​ 7,645 ​ 7,719 ​ Machinery and equipment ​ 207,595 ​ 211,666 ​ Furniture, fixtures, and automobiles ​ 27,123 ​ 26,482 ​ Construction in progress ​ 40,057 ​ 43,981 ​ Total property, plant, and equipment ​ 437,476 ​ 444,202 ​ Less accumulated depreciation ​ (194,552) ​ (184,147) ​ Total property, plant, and equipment, net ​ $ 242,924 ​ $ 260,055 ​

Accounts Payable and Accrued _2

Accounts Payable and Accrued Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Accounts Payable and Accrued Liabilities.
Schedule of accounts payable and accrued liabilities	​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ 2021 ​ 2020 ​ (in thousands) Accrued customer fees and rebates $ 11,581 ​ $ 9,029 Accrued payroll and related benefits ​ 27,324 ​ ​ 24,597 Accrued product returns, current portion ​ 14,823 ​ ​ 10,190 Accrued loss on firm purchase commitments ​ 3,449 ​ ​ 1,223 Accrued litigation and settlements ​ — ​ ​ 13,780 Other accrued liabilities ​ 10,076 ​ ​ 12,328 Total accrued liabilities 67,253 ​ 71,147 Accounts payable 21,658 ​ 24,357 Total accounts payable and accrued liabilities $ 88,911 ​ $ 95,504

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Debt
Schedule of debt	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 ​ 2020 ​ ​ (in thousands) Line of Credit Facilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Line of credit facility with China Everbright Bank - closed June 2021 ​ $ — ​ $ 764 ​ Line of credit facility with China Merchant Bank ​ ​ — ​ ​ 382 ​ Line of credit facility with Bank of Nanjing - deconsolidated (see Note 3) ​ ​ — ​ ​ 153 ​ Line of credit facility with Cathay Bank - closed in August 2021 ​ — ​ — ​ Line of credit facility with East West Bank - closed in August 2021 ​ ​ — ​ ​ — ​ Equipment line of credit facility with East West Bank - closed in August 2021 ​ ​ — ​ ​ 3,216 ​ Revolving line of credit facility with Capital One N.A. due August 2026 ​ ​ — ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ Term Loan ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Term loan with Capital One N.A. due August 2026 ​ ​ 70,000 ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ Mortgage Loans ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mortgage payable with East West Bank paid off May 2021 ​ ​ — ​ ​ 3,306 ​ Mortgage payable with East West Bank paid off August 2021 ​ ​ — ​ ​ 3,334 ​ Mortgage payable with Cathay Bank paid off August 2021 ​ — ​ 7,268 ​ Mortgage payable with East West Bank due June 2027 ​ ​ 8,393 ​ ​ 8,510 ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment Loans ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment loan with East West Bank paid off June 2021 ​ ​ — ​ ​ 612 ​ Equipment loan with East West Bank paid off August 2021 ​ ​ — ​ ​ 4,000 ​ Equipment loan with East West Bank paid off August 2021 ​ ​ — ​ ​ 5,254 ​ ​ ​ ​ ​ ​ ​ ​ ​ Other Loans and Payment Obligations ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Acquisition loan with Cathay Bank paid off August 2021 ​ — ​ 8,710 ​ French government loan paid off July 2021 ​ ​ — ​ ​ 64 ​ French government loans due December 2026 ​ ​ 339 ​ ​ 350 ​ ​ ​ ​ ​ ​ ​ ​ ​ Equipment under Finance Leases ​ 471 ​ 526 ​ Total debt ​ 79,203 ​ 46,449 ​ Less current portion of long-term debt ​ 2,256 ​ 12,263 ​ Less: Loan issuance costs ​ ​ 1,395 ​ ​ 84 ​ Long-term debt, net of current portion and unamortized debt issuance costs ​ $ 75,552 ​ $ 34,186 ​

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2021
Income Taxes
Summary of provision (benefit) for income taxes	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2021 2020 2021 2020 ​ ​ (in thousands) Income before taxes ​ $ 37,646 ​ $ 7,078 ​ $ 56,977 ​ $ 11,379 ​ Income tax provision ​ ​ 6,686 ​ 2,285 ​ ​ 13,436 ​ 4,490 ​ Net income ​ $ 30,960 ​ $ 4,793 ​ $ 43,541 ​ $ 6,889 ​ Income tax provision as a percentage of income before income taxes ​ ​ 17.8 % 32.3 % ​ 23.6 % 39.5 %

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity
Schedule of key assumptions to determine fair value of options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ Average volatility 41.4 % 43.7 % 42.1 % 43.1 % ​ Average risk-free interest rate 1.1 % 0.5 % 1.2 % 0.8 % ​ Weighted-average expected life in years 6.3 ​ 6.3 ​ 6.1 ​ 5.7 ​ ​ 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 1,436,929 ​ ​ 18.25 ​ ​ ​ ​ ​ ​ Options exercised (899,436) ​ ​ 13.49 ​ ​ ​ ​ ​ ​ Options cancelled (155,784) ​ ​ 17.02 ​ ​ ​ ​ ​ ​ Options expired (56,826) ​ ​ 14.67 ​ ​ ​ ​ ​ ​ Outstanding as of September 30, 2021 8,905,358 ​ $ 15.65 ​ 5.34 ​ $ 33,500 ​ Exercisable as of September 30, 2021 6,021,669 ​ $ 15.11 ​ 3.90 ​ $ 26,145 ​ (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 September 30, 2021.
Schedule of information relating to options grants	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands, except per share data) Weighted-average grant date fair value per option share ​ $ 8.00 ​ $ 8.64 ​ $ 7.62 ​ $ 5.50 ​ Intrinsic value of options exercised ​ 2,176 ​ 1,687 ​ 5,292 ​ 8,661 ​ Cash received from options exercised ​ 3,953 ​ 3,195 ​ 12,122 ​ 23,534 ​ Total fair value of the options vested during the period ​ 112 ​ 121 ​ 8,162 ​ 9,965 ​
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 1,436,929 ​ 7.62 ​ Options vested (1,223,108) ​ 6.67 ​ Options forfeited (155,784) ​ 6.98 ​ Non-vested as of September 30, 2021 2,883,689 ​ 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 600,207 ​ $ 10,941 ​ RSUs forfeited (64,030) ​ ​ ​ ​ RSUs vested (2) (493,007) ​ ​ ​ ​ RSUs outstanding at September 30, 2021 1,199,688 ​ ​ ​ ​ (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, 167,034 shares of common stock were surrendered to fulfill tax withholding obligations. ​
Schedule of recorded share-based compensation expense under all plans	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 ​ 2020 ​ 2021 2020 ​ ​ (in thousands) Cost of revenues $ 889 $ 947 $ 2,967 $ 3,276 ​ Operating expenses: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Selling, distribution, and marketing ​ 164 ​ 120 ​ 438 ​ 350 ​ General and administrative ​ 2,533 ​ 2,899 ​ 10,069 ​ 11,170 ​ Research and development ​ 333 ​ 404 ​ 1,363 ​ 1,369 ​ Total share-based compensation ​ $ 3,919 ​ $ 4,370 ​ $ 14,837 ​ $ 16,165 ​

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Gains and (losses) of intercompany foreign currency transactions	$ (900)	$ 1,400	$ (1,900)	$ 1,400
Income tax expense allocated to other comprehensive income	0	400	0	400
Selling, distribution, and marketing expense	4,745	3,673	13,411	10,993
Restricted cash	235		235		$ 1,865
Certificates of deposit	2,200		2,200		$ 2,200
Finished Pharmaceutical Products | Primatene Mist
Advertising expense	$ 2,300	$ 1,500	$ 6,400	$ 3,900

ANP Restructuring (Details)

ANP Restructuring (Details) - USD ($) $ in Thousands	1 Months Ended				3 Months Ended	9 Months Ended
	Aug. 31, 2021	Jul. 31, 2021	May 31, 2021	Jul. 31, 2018	Sep. 30, 2021	Sep. 30, 2021
Restructuring and Related Cost [Line Items]
Gain on deconsolidation of subsidiary						$ 13,587
Equity method investment					$ 4,193	$ 4,193
Hanxin
Restructuring and Related Cost [Line Items]
Ownership after transaction		20.00%			14.00%	14.00%
Gain on deconsolidation of subsidiary					$ 13,600	$ 13,600
Deconsolidation, revaluation of retained investment, gain					2,700	2,700
Equity method investment					$ 4,200	$ 4,200
ANP
Restructuring and Related Cost [Line Items]
Ownership percentage		100.00%
ANP
Restructuring and Related Cost [Line Items]
Proceeds from private placement				$ 56,300
Equity interest retained post private placement				58.00%
Percentage of ownership interest acquired	15.00%		18.00%
Payments for additional ownership interest	$ 22,500		$ 29,400
Percentage of additional ownership interest from shares repurchase			10.00%
Ownership after transaction	100.00%		85.00%
ANP | Hanxin
Restructuring and Related Cost [Line Items]
Decrease in ownership percentage			80.00%
Hanxin
Restructuring and Related Cost [Line Items]
Ownership after transaction					14.00%	14.00%

Revenue Recognition (Analysis o

Revenue Recognition (Analysis of the Chargeback Provision) (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Beginning balance	$ 20,380	$ 21,644	$ 21,644
Provision for chargebacks and rebates	151,174	110,763
Credits and payments issued to third parties	(154,143)	(113,576)
Ending balance	17,411	$ 18,831	20,380
Accounts Receivable, Net
Provision for chargebacks and rebates	13,500		16,400
Accounts Payable and Accrued Liabilities
Provision for chargebacks and rebates	$ 3,900		$ 4,000

Revenue Recognition (Analysis_2

Revenue Recognition (Analysis of Product Return Liability) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Aggregate product return rate	1.70%	1.30%
Return accrual included in accounts payable and accrued liabilities	$ 14,823		$ 10,190
Return accrual included in other long-term liabilities	4,900		$ 4,000
Product returns
Beginning balance	14,204	$ 10,339
Provision for product returns	11,714	9,084
Credits issued to third parties	(6,183)	(6,731)
Ending balance	$ 19,735	$ 12,692

Income (Loss) per Share Attri_3

Income (Loss) per Share Attributable to Amphastar Pharmaceuticals, Inc. Stockholders (Narrative) (Details) - Stock Options - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Shares	1,885,093	1,271,347	2,045,878	1,928,629
Antidilutive Securities Excluded from Computation of Earnings Per Share, Exercise Price of Excluded Securities	$ 20.86	$ 21.35	$ 20.74	$ 20.84

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						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Basic and dilutive numerator:
Net Income (Loss) Attributable to Parent	$ 29,548	$ 7,767	$ 5,041	$ 3,919	$ (192)	$ 3,949	$ 42,356	$ 7,676
Denominator:
Weighted-average shares outstanding-basic	48,022			47,496			47,758	46,886
Net effect of dilutive securities:
Incremental shares from equity awards	1,987			2,352			1,935	2,036
Weighted-average shares outstanding - diluted	50,009			49,848			49,693	48,922
Net income (loss) per share - basic	$ 0.62			$ 0.08			$ 0.89	$ 0.16
Net income (loss) per share - diluted	$ 0.59			$ 0.08			$ 0.85	$ 0.16

Segment Reporting (Selected Fin

Segment Reporting (Selected Financial Information by Reporting Segment) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)segment	Sep. 30, 2020USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment			2
Net revenues:
Net revenues	$ 112,198	$ 83,431	$ 316,881	$ 253,925
Gross profit (loss):
Gross Profit	51,183	36,508	143,505	106,508
Operating expenses	26,414	32,991	97,870	98,433
Income (loss) from operations	24,769	3,517	45,635	8,075
Non-operating income (expenses)	12,877	3,561	11,342	3,304
Income (loss) before income taxes	37,646	7,078	56,977	11,379
Finished Pharmaceutical Products
Net revenues:
Net revenues	108,990	81,335	301,594	243,568
Gross profit (loss):
Gross Profit	54,602	39,546	149,502	113,793
API
Net revenues:
Net revenues	3,208	2,096	15,287	10,357
Gross profit (loss):
Gross Profit	$ (3,419)	$ (3,038)	$ (5,997)	$ (7,285)

Segment Reporting (Summary of N

Segment Reporting (Summary of Net Revenues by Product Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net revenues	$ 112,198	$ 83,431	$ 316,881	$ 253,925
Finished Pharmaceutical Products
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net revenues	108,990	81,335	301,594	243,568
Finished Pharmaceutical Products | Enoxaparin
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net revenues	8,034	11,647	28,020	31,033
Finished Pharmaceutical Products | Lidocaine
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net revenues	11,649	10,657	32,314	28,922
Finished Pharmaceutical Products | Phytonadione
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net revenues	11,591	10,470	31,577	32,188
Finished Pharmaceutical Products | Naloxone
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net revenues	8,028	8,739	20,994	26,337
Finished Pharmaceutical Products | Epinephrine
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net revenues	13,892	5,370	38,662	16,317
Finished Pharmaceutical Products | Primatene Mist
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net revenues	16,561	12,988	51,624	38,333
Finished Pharmaceutical Products | Glucagon
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net revenues	12,189		32,304
Finished Pharmaceutical Products | Other Finished Pharmaceutical Products
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Net revenues	$ 27,046	$ 21,464	$ 66,099	$ 70,438

Segment Reporting (Depreciation

Segment Reporting (Depreciation and Amortization Expense by Reporting Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Depreciation and amortization expense	$ 2,504	$ 2,456	$ 7,626	$ 6,530
Finished Pharmaceutical Products
Segment Reporting Information [Line Items]
Depreciation and amortization expense	1,534	1,408	4,429	4,325
API
Segment Reporting Information [Line Items]
Depreciation and amortization expense	$ 970	$ 1,048	$ 3,197	$ 2,205

Segment Reporting (Summary of R

Segment Reporting (Summary of Revenues and Long-Lived Assets by Geographic Region) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	$ 112,198	$ 83,431	$ 316,881	$ 253,925
Long-Lived Assets	271,015		271,015		$ 280,709
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	107,829	79,407	302,192	242,370
Long-Lived Assets	134,684		134,684		129,401
CHINA
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	2,554	1,959	4,801	2,482
Long-Lived Assets	89,385		89,385		98,538
FRANCE
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	1,815	$ 2,065	9,888	$ 9,073
Long-Lived Assets	$ 46,946		$ 46,946		$ 52,770

Customer and Supplier Concent_3

Customer and Supplier Concentration (Details) - Customer Concentration Risk [Member] - item	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 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 Revenue
Revenue, Major Customer [Line Items]
Number of major customers	3	3	3	3
AmerisourceBergen | Accounts Receivable, Net
Revenue, Major Customer [Line Items]
Major Customers			15.00%		9.00%
AmerisourceBergen | Net Revenue
Revenue, Major Customer [Line Items]
Major Customers	25.00%	23.00%	24.00%	23.00%
Cardinal Health | Accounts Receivable, Net
Revenue, Major Customer [Line Items]
Major Customers			20.00%		17.00%
Cardinal Health | Net Revenue
Revenue, Major Customer [Line Items]
Major Customers	18.00%	17.00%	16.00%	18.00%
McKesson | Accounts Receivable, Net
Revenue, Major Customer [Line Items]
Major Customers			23.00%		24.00%
McKesson | Net Revenue
Revenue, Major Customer [Line Items]
Major Customers	21.00%	21.00%	20.00%	22.00%

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Values of the Company's Financial Assets and Liabilities) (Details) - Recurring Basis - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate and municipal bonds	$ 3,039	$ 3,855
Fair value measurement	92,443	74,817
Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps related to variable rate loans	(279)	(902)
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	5,102	9,089
Restricted short-term investments	2,200	2,200
Money market
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	82,146	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	82,381	60,575
Level 1 | Money market
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	82,146	58,710
Restricted cash	235	1,865
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate and municipal bonds	3,039	3,855
Fair value measurement	10,062	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	(279)	(902)
Level 2 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	5,102	9,089
Restricted short-term investments	$ 2,200	$ 2,200

Investments (Held-to_Maturity)

Investments (Held-to_Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 3,040	$ 3,857
Gross Unrealized Losses	(1)	(2)
Fair Value	3,039	3,855
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	513	1,560
Gross Unrealized Losses	(1)	(1)
Fair Value	512	1,559
Municipal Bonds [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,527	2,297
Gross Unrealized Losses		(1)
Fair Value	$ 2,527	$ 2,296

Investments (Equity Method Inve

Investments (Equity Method Investment) (Details)	Sep. 30, 2021	Jul. 31, 2021
Hanxin
Restructuring and Related Cost
Equity Method Investment, Ownership Percentage	14.00%	20.00%

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets (Summary of Intangible Assets) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Definite-lived intangible assets
Weighted-Average Life (Years)	12 years	12 years
Finite-Lived Intangible Assets, Gross	$ 12,442	$ 12,587
Accumulated Amortization	5,861	5,137
Finite-Lived Intangible Assets, Net	6,581	7,450
Indefinite-lived intangible assets
Goodwill recognized	3,386	3,940	$ 3,634
Subtotal, Original Cost	32,611	33,165
Subtotal, Net Book Value	32,611	33,165
Balance, Original Cost	45,053	45,752
Balance, Net Book Value	39,192	40,615
Finished Pharmaceutical Products
Indefinite-lived intangible assets
Goodwill recognized	3,386	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	329	297
Finite-Lived Intangible Assets, Net	$ 157	$ 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	667	617
Finite-Lived Intangible Assets, Net	$ 1,873	$ 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	$ 9,416	$ 9,561
Accumulated Amortization	4,865	4,223
Finite-Lived Intangible Assets, Net	$ 4,551	$ 5,338

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets (Summary of Changes in the Carrying Amount of Goodwill) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Beginning balance	$ 3,940	$ 3,634
Currency translation and other adjustments	(180)	306
Ending balance	3,386	$ 3,940
ANP
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down	$ (374)

Inventories (Details)

Inventories (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Raw materials and supplies	$ 45,752		$ 45,752		$ 47,051
Work in process	37,555		37,555		37,257
Finished goods	16,933		16,933		12,523
Total inventory, net	100,240		100,240		$ 96,831
Inventory adjustment to reflect net realizable value	$ 6,100		17,000
Enoxaparin
Inventory, Firm Purchase Commitment, Loss			$ 3,500	$ 4,200
ANP | Crude Heparin
Inventory adjustment to reflect net realizable value		$ 2,500		$ 12,700

Property, Plant, and Equipmen_2

Property, Plant, and Equipment (Summary of Property, Plant, and Equipment) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	$ 437,476	$ 444,202
Less accumulated depreciation and amortization	(194,552)	(184,147)
Total property, plant, and equipment, net	242,924	260,055
Buildings
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	127,700	124,326
Leasehold improvement
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	27,356	30,028
Land
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	7,645	7,719
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	207,595	211,666
Furniture, fixtures, and automobiles
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	27,123	26,482
Construction in progress
Property, Plant and Equipment [Line Items]
Total property, plant, and equipment	$ 40,057	$ 43,981

Accounts Payable and Accrued _3

Accounts Payable and Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounts Payable and Accrued Liabilities.
Accrued customer fees and rebates	$ 11,581	$ 9,029
Accrued payroll and related benefits	27,324	24,597
Accrued product returns, current portion	14,823	10,190
Accrued loss on firm purchase commitments	3,449	1,223
Accrued litigation settlement		13,780
Other accrued liabilities	10,076	12,328
Total accrued liabilities	67,253	71,147
Accounts payable	21,658	24,357
Total accounts payable and accrued liabilities	$ 88,911	$ 95,504

Debt (Schedule of Debt) (Detail

Debt (Schedule of Debt) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument
Unamortized Debt Issuance Expense	$ 1,395	$ 84
Equipment under Finance Leases	471	526
Total debt	79,203	46,449
Less current portion of long-term debt and finance leases	2,256	12,263
Long-term debt, net of current portion and unamortized debt costs	75,552	34,186
Mortgage Payable - Paid off May 2021 | East West Bank
Debt Instrument
Long Term Debt		3,306
Equipment Loan - Paid off June 2021 | East West Bank
Debt Instrument
Long Term Debt		612
Equipment Loan - Paid off August 2021 | East West Bank
Debt Instrument
Long Term Debt		4,000
Equipment Loan - Paid off August 2021 | East West Bank
Debt Instrument
Long Term Debt		5,254
Mortgage Payable - Paid off August 2021 | East West Bank
Debt Instrument
Long Term Debt		3,334
Mortgage Payable - Due June 2027 | East West Bank
Debt Instrument
Long Term Debt	8,393	8,510
Mortgage Payable - Paid off August 2021 | Cathay Bank
Debt Instrument
Long Term Debt		7,268
Acquisition Loan - Paid off August 2021 | Cathay Bank
Debt Instrument
Long Term Debt		8,710
Line of credit - Closed June 2021 | China Everbright Bank
Debt Instrument
Long Term Debt		764
Line of Credit - Due March 2023 | China Merchant Bank
Debt Instrument
Long Term Debt		382
Line of Credit - deconsolidated | Bank of Nanjing
Debt Instrument
Long Term Debt		153
Equipment Line of Credit - Closed August 2021 | East West Bank
Debt Instrument
Long Term Debt		3,216
Term Loan - Due August 2026 | Capital One, N.A.
Debt Instrument
Long Term Debt	70,000
French Government Loan - Due July 2021 | Seine-Normandie Water Agency
Debt Instrument
Long Term Debt		64
French Government Loan 4 - Due December 2026 | Seine-Normandie Water Agency
Debt Instrument
Long Term Debt	$ 339	$ 350

Debt (Narrative) (Details)

Debt (Narrative) (Details) - USD ($)	Aug. 04, 2021	Sep. 30, 2020	Sep. 30, 2021	Aug. 05, 2021
Debt
Proceeds from borrowing under lines of credit		$ 1,072,000
Credit Agreement | Capital One, N.A.
Debt
Maximum borrowing capacity	$ 140,000,000
Credit Agreement | Capital One, N.A. | In the first two years
Debt
Debt Instrument, Annual Principal Payment	1,800,000
Credit Agreement | Capital One, N.A. | Starting in the third year
Debt
Debt Instrument, Annual Principal Payment	3,500,000
Credit Agreement | Capital One, N.A. | Starting in the fifth year
Debt
Debt Instrument, Annual Principal Payment	3,900,000
Credit Agreement | Capital One, N.A. | Interest rate swaps
Debt
Notional Amount				$ 55,000,000
Interest rate swap, fair value				$ 0.93
Term Loan | Capital One, N.A.
Debt
Debt Instrument, Interest Rate, Stated Percentage			1.84%
Borrowings	70,000,000
Loan issuance costs			$ 1,400,000
Revolving Credit Facility | Capital One, N.A.
Debt
Maximum borrowing capacity	$ 70,000,000
Minimum | Term Loan | Capital One, N.A. | LIBOR
Debt
Debt Instrument, Basis Spread on Variable Rate	0.50%
Maximum | Term Loan | Capital One, N.A. | LIBOR
Debt
Debt Instrument, Basis Spread on Variable Rate	2.50%

Income Taxes (Summary of Income

Income Taxes (Summary of Income Before Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income (loss) before income taxes:
Income (loss) before income taxes	$ 37,646	$ 7,078	$ 56,977	$ 11,379
Income tax provision (benefit)	6,686	2,285	13,436	4,490
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 30,960	$ 4,793	$ 43,541	$ 6,889
Income tax provision as a percentage of income before income taxes	17.80%	32.30%	23.60%	39.50%
Other Effective Tax Rate Provision (Benefit)	$ 100	$ 200	$ 300	$ 400

Stockholders' Equity (Share Buy

Stockholders' Equity (Share Buyback Program) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Aug. 03, 2021
Equity, Class of Treasury Stock [Line Items]
Treasury Stock, Value, Acquired, Cost Method	$ 6,094	$ 5,560	$ 3,783	$ 4,329	$ 5,756	$ 10,950
November 2014 Share Repurchase Plan
Equity, Class of Treasury Stock [Line Items]
Stock buyback program, authorized amount	$ 160,000						$ 160,000
Increase authorized for share buyback program									$ 20,000
Treasury Stock, Shares, Acquired (in Shares)	317,212			214,256			820,637	1,190,362
Treasury Stock, Value, Acquired, Cost Method	$ 6,100			$ 4,300			$ 15,400	$ 21,000

Stockholders' Equity (The 2015

Stockholders' Equity (The 2015 Equity Incentive Plan) (Details) - The 2015 Equity Incentive Plan - shares	Jan. 01, 2021	Sep. 30, 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)		5,997,738
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 ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation		$ 3,919	$ 4,370	$ 14,837	$ 16,165
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)	83,354			890,904
Weighted-Average Purchase Price (In Dollars per Share)	$ 15.25
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in Shares)		1,109,096		1,109,096
Allocated share based compensation		$ 200	$ 100	$ 500	$ 500

Stockholders' Equity (Key Assum

Stockholders' Equity (Key Assumptions Used in Determining Fair Value of Options Granted) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stockholders' Equity
Average volatility	41.40%	43.70%	42.10%	43.10%
Risk-free interest rate	1.10%	0.50%	1.20%	0.80%
Weighted-average expected life in years	6 years 3 months 18 days	6 years 3 months 18 days	6 years 1 month 6 days	5 years 8 months 12 days
Dividend yield rate	0.00%	0.00%	0.00%	0.00%

Stockholders' Equity (Summary o

Stockholders' Equity (Summary of Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Apr. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Options
Outstanding Options, Beginning of period				8,580,475
Options granted				1,436,929
Options exercised				(899,436)
Options cancelled				(155,784)
Options expired				(56,826)
Outstanding Options, End of period		8,905,358		8,905,358
Exercisable at the end of period		6,021,669		6,021,669
Weighted-Average Exercise Price
Outstanding Exercise Price (in dollars per share)				$ 15
Options granted (in dollars per share)				18.25
Options exercised (in dollars per share)				13.49
Options cancelled (in dollars per share)				17.02
Options expired (in dollars per share)				14.67
Outstanding Exercise Price (in dollars per share)		$ 15.65		15.65
Exercisable at the end of period (in dollars per share)		$ 15.11		$ 15.11
Additional Disclosures
Contractual term				5 years 4 months 2 days
Outstanding Intrinsic Value		$ 33,500		$ 33,500
Exercisable remaining contractual term (in Years)				3 years 10 months 24 days
Exercisable aggregate intrinsic value		26,145		$ 26,145
Allocated share based compensation		3,919	$ 4,370	14,837	$ 16,165
Employee Stock Option
Additional Disclosures
Allocated share based compensation		$ 1,900	$ 1,900	$ 6,200	7,100
Employee Stock Option | President, General Counsel and member of board of directors
Additional Disclosures
Allocated share based compensation					$ 700
Vesting (percent)	80.00%

Stockholders' Equity (Informati

Stockholders' Equity (Information Relating to Option Grants and Exercises) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stockholders' Equity
Weighted-average grant date fair value (in Dollars per share)	$ 8	$ 8.64	$ 7.62	$ 5.50
Intrinsic value of options exercised	$ 2,176	$ 1,687	$ 5,292	$ 8,661
Cash received	3,953	3,195	12,122	23,534
Total fair value of the options vested during the period	$ 112	$ 121	$ 8,162	$ 9,965

Stockholders' Equity (Summary_2

Stockholders' Equity (Summary of Nonvested Options) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Options
Nonvested at beginning of period			2,825,652
Options granted			1,436,929
Options vested			(1,223,108)
Options forfeited			(155,784)
Nonvested at end of period	2,883,689		2,883,689
Weighted-Average Grant Date Fair Value
Nonvested at beginning of period (in dollars per share)			$ 6.50
Options granted (in dollars per share)	$ 8	$ 8.64	7.62	$ 5.50
Options vested (in dollars per share)			6.67
Options forfeited (in dollars per share)			6.98
Nonvested at end of period (in dollars per share)	$ 6.96		$ 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	$ 14.1		$ 14.1
Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition			2 years 7 months 6 days

Stockholders' Equity (Restricte

Stockholders' Equity (Restricted Stock Units) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended
	Apr. 30, 2020	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term						5 years 4 months 2 days
Allocated share based compensation		$ 3,919		$ 4,370		$ 14,837	$ 16,165
Share-based Payment Arrangement, Plan Modification, Incremental Cost			$ 2,300		$ 2,300
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		$ 1,900		$ 2,000		$ 6,200	8,000
Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition						2 years 7 months 6 days
Share-based Compensation Arrangement by Share-based Payment Award, Restricted Stock Units, Number of Shares of Common Stock Per Award (in Shares)		1				1
Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options		$ 15,000				$ 15,000
President, General Counsel and member of board of directors | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation							$ 1,600
Vesting (percent)	80.00%

Stockholders' Equity (Informa_2

Stockholders' Equity (Information Relating to RSU Grants and Deliveries) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 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	600,207
RSUs forfeited	(64,030)
RSUs vested	(493,007)
Total RSUs outstanding at the end of the period	1,199,688
Stock surrendered to fulfill tax withholding obligations	167,034
Restricted Stock Units Issued as Compensation
Total Fair Market Value of RSUs Issued
RSUs granted (in Dollars) | $	$ 10,941

Stockholders' Equity (The 2018

Stockholders' Equity (The 2018 ANP Equity Incentive Plan) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted					1,436,929
Options outstanding	8,905,358				8,905,358		8,580,475
Number of vested options					1,223,108
Number of unvested options	2,883,689				2,883,689		2,825,652
Vested options cancelled					155,784
Unvested options cancelled					155,784
Contractual term					5 years 4 months 2 days
Plan modification, share-based compensation expense		$ 2,300		$ 2,300
Allocated share based compensation	$ 3,919		$ 4,370		$ 14,837	$ 16,165
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Plan modification, share-based compensation expense		$ 1,800		$ 1,800
Allocated share based compensation	$ 2,533		2,899		$ 10,069	11,170
The 2018 ANP Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation			$ 200			$ 500
The 2018 ANP Equity Incentive Plan | Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding	4,091,080				4,091,080
Number of vested options	1,944,771
Number of unvested options	2,146,309				2,146,309
Options fair value	$ 800
Options cancelled	927,800
Vested options cancelled	56,925
Unvested options cancelled	870,875
The 2018 ANP Equity Incentive Plan | Employees | The 2018 ANP Equity Incentive Plan Termination
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding		5,018,880		5,018,880
The 2015 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost not yet recognized	$ 500				$ 500
The 2015 Equity Incentive Plan | Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term	10 years
The 2015 Equity Incentive Plan | Employees | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
The 2015 Equity Incentive Plan | Employees | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	2 years

Stockholders' Equity (Share-Bas

Stockholders' Equity (Share-Based Compensation Expense Included in the Statement of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	$ 3,919	$ 4,370	$ 14,837	$ 16,165
Cost of revenues
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	889	947	2,967	3,276
Selling, distribution and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	164	120	438	350
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	2,533	2,899	10,069	11,170
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation	$ 333	$ 404	$ 1,363	$ 1,369

Employee Benefits (Details)

Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 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	$ 0.4	$ 1.5	$ 1.4
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	0.30%		0.30%		0.30%
Defined Benefit Plan, Benefit Obligation	$ 2.9		$ 2.9
Pension Cost	0	$ 0	0	$ 0
Deferred compensation plan assets	2.7		2.7		$ 1.6
Deferred compensation plan liabilities	$ 2.7		$ 2.7		$ 1.7

Commitments and Contingencies (

Commitments and Contingencies (Purchase Commitments) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Commitments to Purchase Equipment and Raw Materials
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Long-term Purchase Commitment, Amount	$ 56.2

Related-Party Transactions (Det

Related-Party Transactions (Details) - USD ($) $ in Millions	1 Months Ended
	Sep. 30, 2021	Aug. 31, 2021	May 31, 2021
Hanxin
Related Party Transaction [Line Items]
Ownership after transaction	14.00%
Hanxin | Service Fee
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party	$ 2.5
ANP
Related Party Transaction [Line Items]
Ownership after transaction		100.00%	85.00%

Litigation (Details)

Litigation (Details) - USD ($) $ in Thousands	Jun. 30, 2021	May 03, 2021	Apr. 05, 2021	Nov. 13, 2020	May 31, 2021	Jun. 30, 2021	Dec. 31, 2020	Mar. 31, 2021
Loss Contingencies [Line Items]
Estimated Litigation Liability							$ 13,780
Ramirez vs Amphastar Pharmaceuticals, Inc
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]
Litigation Settlement, Amount		$ 4,400			$ 17,200
Settled Litigation [Member] | Amphastar Pharmaceuticals, Inc. Vs Aventis Pharma, SA
Loss Contingencies [Line Items]
Litigation Settlement, Amount	$ 14,500			$ 12,100			$ 12,800
Costs and expenses				$ 700
Litigation settlement accrual amount increase						$ 1,700