Apergy S-4 15 Nov 18 Registration of securities issued in business combination transactions Financial data

Document and Entity Information

Document and Entity Information	9 Months Ended
	Sep. 30, 2018
Document And Entity Information [Abstract]
Document Type	S4
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Trading Symbol	apy
Entity Registrant Name	Apergy Corporation
Entity Central Index Key	1,723,089
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended																	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Lease and other revenue	$ 12,894			$ 6,657														$ 35,993	$ 19,093
Total revenue	316,468	$ 264,498		258,654		$ 256,161		$ 230,278		$ 201,176		$ 185,455		$ 168,535		$ 196,171		906,318	745,093	$ 1,009,591	$ 751,337	$ 1,076,680
Cost of goods and services	202,734			173,880														594,605	500,329	691,124	556,009	742,041
Gross profit	113,734	73,703		84,774		84,630		75,360		61,012		47,254		32,610		54,452		311,713	244,764	318,467	195,328	334,639
Selling, general and administrative expense	69,022			54,828														194,568	162,359	219,517	205,409	245,723
Operating income (loss)																				98,950	(10,081)	88,916
Interest expense, net	10,584			79														16,813	199
Other expense, net	910			2,941														3,724	7,929	9,666	8,753	11,651
Income (loss) before income taxes	33,218			26,926														96,608	74,277	89,284	(18,834)	77,265
Provision for (benefit from) income taxes	7,723			8,241														24,324	22,973	(22,284)	(8,043)	24,131
Net income (loss)	25,495	60,264		18,685		19,033		13,586		4,167		(2,154)		(10,294)		(2,510)		72,284	51,304	111,568	(10,791)	53,134
Net income (loss) attributable to noncontrolling interest	232			264														295	860	930	1,851	1,436
Net income	$ 25,263	$ 60,194		$ 18,421		$ 18,754		$ 13,269		$ 3,769		$ (2,503)		$ (10,872)		$ (3,036)		$ 71,989	$ 50,444	$ 110,638	$ (12,642)	$ 51,698
Earnings per share, basic	$ 0.33	$ 0.78	[1]	$ 0.24	[1]	$ 0.24	[1]	$ 0.17	[1]	$ 0.05	[1]	$ (0.03)	[1]	$ (0.14)	[1]	$ (0.04)	[1]	$ 0.93	$ 0.65
Earnings per share, diluted	$ 0.33	$ 0.77	[1]	$ 0.24	[1]	$ 0.24	[1]	$ 0.17	[1]	$ 0.05	[1]	$ (0.03)	[1]	$ (0.14)	[1]	$ (0.04)	[1]	$ 0.93	$ 0.65
Weighted-average number of shares outstanding, basic	77,340			77,340														77,340	77,340
Weighted-average number of shares outstanding, diluted	77,569			77,890														77,742	77,890
Product [Member]
Revenue	$ 283,103			$ 235,848														$ 808,311	$ 679,837
Service [Member]
Revenue	$ 20,471			$ 16,149														$ 62,014	$ 46,163
[1]	On May 9, 2018, 77,339,828 shares of our common stock were distributed to Dover stockholders in conjunction with the Separation. For comparative purposes, we have assumed the shares issued in conjunction with the Separation to be outstanding as of the beginning of each period prior to the Separation. In addition, we have assumed the potential dilutive securities outstanding as of May 8, 2018, were outstanding and fully dilutive in each of the periods prior to the Separation.

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended				9 Months Ended				12 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 25,495		$ 18,685		$ 72,284		$ 51,304		$ 111,568	$ (10,791)	$ 53,134
Net income (loss) attributable to Apergy	25,263		18,421		71,989		50,444		110,638	(12,642)	51,698
Foreign currency translation adjustments [Abstract]
Foreign currency translation adjustments	(515)	[1]	5,303	[1]	(9,080)	[1]	6,895	[1]	4,358	953	(11,691)
Pension and other post-retirement benefit plans:
Net actuarial gain arising during period					170				2,598	(123)	(485)
Prior service cost											(6)
Reclassification adjustment of net actuarial loss included in net income	86		67		181		199		257	234	221
Reclassification adjustment for settlement losses included in net income	353				353
Amortization of prior service costs included in net periodic pension cost									1	1	1
Total pension and other post-retirement benefit plans	439	[2]	67	[2]	704	[2]	199	[2]	2,856	112	(269)
Other comprehensive income (loss)	(76)		5,370		(8,376)		7,094		7,214	1,065	(11,960)
Comprehensive income	25,419		24,055		63,908		58,398
Comprehensive income attributable to noncontrolling interest	232		264		295		860		930	1,851	1,436
Comprehensive income (loss)	$ 25,187		$ 23,791		$ 63,613		$ 57,538		$ 117,852	$ (11,577)	$ 39,738
[1]	Net of income tax (expense) benefit of nil for the three and nine months ended September 30, 2018 and 2017.
[2]	Net of income tax (expense) benefit of $161 and $35 for the three months ended September 30, 2018 and 2017, respectively, and $123 and $102 for the nine months ended September 30, 2018 and 2017, respectively.

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	$ 161	$ 35	$ 123	$ 102	$ 971	$ 42	$ (124)

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 18,014	$ 23,712
Receivables, net of allowances	277,926	202,024
Inventories	219,133	201,591
Prepaid and other current assets	20,824	14,038
Total current assets	535,897	441,365
Property, plant and equipment, net	236,067	211,832
Goodwill	906,766	910,088
Intangible assets, net	297,397	338,510
Other non-current assets	7,229	2,980
Total assets	1,983,356	1,904,775
Current liabilities:
Accounts payable	127,103	98,826
Accrued compensation and employee benefits	36,988	30,289
Accrued expenses and other current liabilities	53,054	21,950
Total current liabilities	217,145	151,065
Long-term debt	687,543	3,742
Deferred income taxes	93,138	96,985
Other long-term liabilities	20,770	12,949
Other liabilities including long term debt		16,691
Total liabilities	1,018,596	264,741
Stockholders' equity:
Common Stock	773
Additional paid-in capital	967,044
Retained earnings	33,257
Net parent investment in Apergy	1,001,074	1,661,700
Accumulated other comprehensive loss	(38,527)	(26,415)
Total stockholders' equity	962,547	1,635,285
Noncontrolling interest	2,213	4,749
Total equity	964,760	1,640,034
Total liabilities and equity	$ 1,983,356	1,904,775
Pro Forma
Stockholders' equity:
Common Stock		774
Additional paid-in capital		948,337
Accumulated other comprehensive loss		(30,495)
Total stockholders' equity		918,616
Noncontrolling interest		4,749
Total equity		$ 923,365

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 5,454	$ 4,753	$ 5,634
Par value of common stock (in dollars per share)	$ 0.01
Common stock, shares authorized (in shares)	2,500,000,000
Common stock, shares issued (in shares)	77,300,000
Common stock, shares outstanding (in shares)	77,300,000

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Net Parent Investment in Apergy	Accum. Other Comp. Loss	Total Parent Company Equity	Non-controlling Interest	Common Stock, Par Value	Common Stock, Capital in excess of par value	Retained Earnings
Balance at Dec. 31, 2014	$ 1,797,040	$ 1,815,910	$ (22,734)	$ 1,793,176	$ 3,864
Net income (loss)	53,134	51,698		51,698	1,436
Other comprehensive income, net of tax	(11,960)		(11,960)	(11,960)
Net transfer to/from Parent Company	(193,049)	(193,049)		(193,049)
Other	(172)				(172)
Balance at Dec. 31, 2015	1,644,993	1,674,559	(34,694)	1,639,865	5,128
Net income (loss)	(10,791)	(12,642)		(12,642)	1,851
Other comprehensive income, net of tax	1,065		1,065	1,065
Net transfer to/from Parent Company	(81,966)	(81,966)		(81,966)
Distributions to noncontrolling interest	(1,727)				(1,727)
Other	(221)				(221)
Balance at Dec. 31, 2016	1,551,353	1,579,951	(33,629)	1,546,322	5,031
Net income (loss)	111,568	110,638		110,638	930
Other comprehensive income, net of tax	7,214		7,214	7,214
Net transfer to/from Parent Company	(28,889)	(28,889)		(28,889)
Distributions to noncontrolling interest	(1,212)				(1,212)
Balance at Dec. 31, 2017	1,640,034	1,661,700	(26,415)	$ 1,635,285	4,749	$ 0	$ 0	$ 0
Cumulative effect of accounting changes	1,300	1,315	(1,315)
Net income (loss)	72,284	38,732			295			33,257
Other comprehensive income, net of tax	(8,376)		(8,376)
Net transfer to/from Parent Company	(738,970)	(736,549)	(2,421)
Reclassification of net parent investment in Apergy		(965,198)					965,198
Issuance of common stock						773	(773)
Stock-based compensation	2,619						2,619
Distributions to noncontrolling interest	(2,720)				(2,720)
Other	(111)				(111)
Balance at Sep. 30, 2018	$ 964,760	$ 0	$ (38,527)		$ 2,213	$ 773	$ 967,044	$ 33,257

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash provided (required) by operating activities:
Net income (loss) attributable to Apergy	$ 71,989	$ 50,444	$ 110,638	$ (12,642)	$ 51,698
Net income	72,284	51,304	111,568	(10,791)	53,134
Adjustments to reconcile net income to net cash provided (required) by operating activities:
Depreciation and amortization			111,879	112,055	119,992
Depreciation	52,814	42,233	58,178	56,068	60,831
Amortization	38,863	40,190
Stock-based compensation	3,129	1,762	2,236	2,293	1,925
(Gain) loss on sale of fixed assets	194	(713)	(934)	(366)	1,463
Provision for losses on accounts receivable (net of recoveries)			954	2,941	2,154
Deferred income taxes	(4,674)	(17,503)	(75,002)	(19,881)	(21,296)
Deferred income taxes and tax credits			(73,433)	(19,994)	(20,270)
Employee benefit plan expense			1,064	1,128	1,114
Contributions to employee benefit plans			(1,876)	(2,649)	(2,667)
Other	5,138	(5,539)	(2,293)	701	8,392
Changes in operating assets and liabilities (net of effects of acquisitions and foreign exchange):
Receivables	(79,533)	(62,203)	(61,274)	26,898	74,825
Inventories	(20,960)	(28,245)	(14,204)	32,912	58,772
Prepaid expenses and other current assets	(5,514)	(4,893)	(5,116)	3,156	(2,388)
Accounts payable	27,776	37,950	29,802	(9,874)	(32,123)
Accrued compensation and employee benefits	13,640	4,965	5,616	(2,122)	(17,772)
Accrued expenses and other current liabilities	24,602	2,927
Leased assets and other	(34,953)	(21,030)	(26,142)	(4,728)	(29,444)
Net cash provided by operating activities	92,806	41,205	76,917	129,709	215,671
Cash provided (required) by investing activities:
Capital expenditures	(45,832)	(29,445)	(41,211)	(26,854)	(31,985)
Proceeds from sale of property, plant and equipment	970	2,616	3,547	2,526	7,884
Acquisition (net of cash and cash equivalents acquired)			(8,842)	(3,700)	(10,000)
Purchase price adjustments on acquisition	53
Additions to intangible assets				(3,700)	(10,000)
Net cash provided (required) by investing activities	(44,809)	(26,829)	(46,506)	(28,028)	(34,101)
Cash provided (required) by financing activities:
Change in borrowings, net			(599)
Proceeds from long-term debt, net of discounts	713,963
Distribution to noncontrolling interest	(2,720)	(1,212)	(1,212)	(1,727)
Payment of debt issue costs	(16,006)
Repayments of long-term debt	(20,000)
Net transfers to Parent	(728,857)	(19,220)	(31,192)	(84,254)	(194,977)
Net cash provided by (required by) financing activities	(53,620)	(20,432)	(33,003)	(85,981)	(194,977)
Effect of exchange rate changes on cash and cash equivalents	(75)	3,476	277	(90)	(531)
Net (decrease) increase in cash and cash equivalents	(5,698)	(2,580)	(2,315)	15,610	(13,938)
Cash and cash equivalents at beginning of period	23,712	26,027	26,027	10,417	24,355
Cash and cash equivalents at end of period	$ 18,014	$ 23,447	23,712	26,027	10,417
Supplemental information - cash paid during the year for:
Income taxes			$ 8,698	$ 7,285	$ 7,808

Basis of Presentation and Separ

Basis of Presentation and Separation	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Separation	NOTE 1 — BASIS OF PRESENTATION AND SEPARATION Apergy Corporation (“Apergy”) is a leading provider of highly engineered equipment and technologies that help companies drill for and produce oil and gas safely and efficiently around the world. Our products provide efficient functioning throughout the lifecycle of a well—from drilling to completion to production. We report our results of operations in the following reporting segments: Production & Automation Technologies and Drilling Technologies. Our Production & Automation Technologies segment offerings consist of artificial lift equipment and solutions, including rod pumping systems, electric submersible pump systems, progressive cavity pumps and drive systems and plunger lifts, as well as a full automation and digital offering consisting of equipment, software and Industrial Internet of Things solutions for downhole monitoring, wellsite productivity enhancement and asset integrity management. Our Drilling Technologies segment offering provides market leading polycrystalline diamond cutters and bearings that result in cost effective and efficient drilling. Separation and Distribution On April 18, 2018, the Dover Corporation (“Dover”) Board of Directors approved the separation of entities conducting its upstream oil and gas energy business within Dover’s Energy segment (the “Separation”) into an independent, publicly traded company named Apergy Corporation. Apergy Corporation was incorporated in Delaware on October 10, 2017, under the name Wellsite Corporation and was renamed Apergy Corporation on February 2, 2018. Apergy Corporation was formed for the purpose of holding entities, assets and liabilities conducting Dover’s upstream oil and gas business within Dover’s Energy segment. In accordance with the separation and distribution agreement, the two companies were separated by Dover distributing to Dover’s stockholders all 77,339,828 shares of common stock of Apergy on May 9, 2018. Each Dover shareholder received one share of Apergy stock for every two shares of Dover stock held at the close of business on the record date of April 30, 2018. In conjunction with the Separation, Dover received a private letter ruling from the Internal Revenue Service to the effect that, based on certain facts, assumptions, representations and undertakings set forth in the ruling, for U.S. federal income tax purposes, the distribution of Apergy common stock was not taxable to Dover or U.S. holders of Dover common stock, except in respect to cash received in lieu of fractional share interests. Following the Separation, Dover retained no ownership interest in Apergy, and each company, as of May 9, 2018, has separate public ownership, boards of directors and management. A registration statement on Form 10, as amended, describing the Separation was filed by Apergy with the U.S. Securities and Exchange Commission (“SEC”) and was declared effective on April 19, 2018. On May 9, 2018, Apergy common stock began “regular-way” Tax Matters Agreement On May 9, 2018, Apergy and Dover entered into a tax matters agreement which governs Apergy’s and Dover’s respective rights, responsibilities and obligations after the Separation with respect to tax liabilities (including taxes, if any incurred as a result of any failure of the Separation or certain related transactions to qualify for tax-free Apergy also agreed to certain covenants that contain restrictions intended to preserve the tax-free • issue or sell stock or other securities (including securities convertible into Apergy stock but excluding certain compensatory arrangements); • cease to actively conduct its business or dispose of assets outside the ordinary course of business; and • enter into certain other corporate transactions which could cause Apergy to undergo a 40% or greater change in its stock ownership. Employee Matters Agreement On May 9, 2018, Apergy and Dover entered into an employee matters agreement which governs the respective rights, responsibilities and obligations of the parties in connection with the Separation with respect to employee-related matters. The employee matters agreement provides for the allocation and treatment of assets and liabilities as applicable, arising out of incentive plans, retirement plans, and employee health and welfare benefit programs, in which Apergy’s employees participated prior to the Separation, and the treatment of outstanding Dover incentive awards. In general, Apergy assumed liabilities related to its current and former employees incurred before the Separation. Dover retained liabilities accrued prior to the Separation related to certain Apergy participants in Dover’s U.S. defined benefit pension plan. As a result of the Separation and effective May 15, 2018, outstanding Dover equity awards held by Apergy employees, other than Dover performance shares, converted into corresponding Apergy equity awards issued under the Apergy Corporation 2018 Equity and Cash Incentive Plan. Generally, each award is subject to the same terms and conditions as were in effect prior to the Separation. Immediately prior to the Separation, outstanding Dover performance shares held by Apergy employees that related to performance periods ending after the Separation were cancelled. In connection with the Separation, we incurred an aggregate principal amount of $715 million of long-term debt, which consisted of a $415 million term loan facility and $300 million of senior notes. Net proceeds from the notes offering, together with borrowings under the term loan facility, were used to make a cash payment of $700 million to Dover and to pay fees and expenses incurred in connection with the Separation. See Note 8 — Debt for additional information. Basis of Presentation Prior to the Separation, our results of operations, financial position and cash flows were derived from the consolidated financial statements and accounting records of Dover and reflect the combined historical results of operations, financial position and cash flows of certain Dover entities conducting its upstream oil and gas energy business within Dover’s Energy segment, including an allocated portion of Dover’s corporate costs. These financial statements have been presented as if such businesses had been combined for all periods prior to the Separation. All intercompany transactions and accounts within Dover were eliminated. The assets and liabilities were reflected on a historical cost basis since all of the assets and liabilities presented were wholly owned by Dover and were transferred within the Dover consolidated group. The statements of income also include expense allocations for certain corporate functions historically performed by Dover and not allocated to its operating segments, including corporate executive management, human resources, information technology, facilities, tax, shared services, finance and legal, including the costs of salaries, benefits and other related costs. These expense allocations were based on direct usage or benefit where identifiable, with the remainder allocated on the basis of revenue, headcount or other measures. These pre-Separation Prior to the Separation, transactions between Apergy and Dover, with the exception of transactions discussed in Note 3 — Related Party Transactions, are reflected in the condensed combined balance sheet as of December 31, 2017, as part of “Net parent investment in Apergy” and in the condensed combined statements of cash flows as a financing activity in “Distributions to Dover Corporation, net.” See Note 3 — Related Party Transactions for additional information. No portion of Dover’s third-party debt was historically held by an Apergy entity or was transferred to Apergy; therefore, no debt was included in the condensed combined balance sheet as of December 31, 2017, and no interest expense was presented in the condensed combined statement of income for the three and nine months ended September 30, 2017. Intercompany notes payable to Dover of $224.5 million as of December 31, 2017, were presented within “Net parent investment in Apergy” because the notes were not settled in cash. Accordingly, no interest expense related to intercompany debt was presented in the condensed combined statements of income for each of the periods presented prior to the Separation. Additionally, our U.S. cash was historically pooled to Dover through intercompany advances and consequently is not reflected on our condensed combined balance sheet as of December 31, 2017. All financial information presented after the Separation represents the consolidated results of operations, financial position and cash flows of Apergy. Accordingly, our results of operations and cash flows consist of the consolidated results of Apergy from May 9, 2018 to September 30, 2018, and the combined results of operations and cash flows for periods prior to May 9, 2018. Our balance sheet as of September 30, 2018, reflects the consolidated balances of Apergy while the December 31, 2017, balance sheet reflects the combined balances of the Dover upstream oil and gas energy businesses that were transferred to Apergy. Our management believes the assumptions underlying these condensed consolidated financial statements, including the assumptions regarding the allocation of corporate expenses from Dover for periods prior to the Separation, are reasonable. The legal transfer of the upstream oil and gas energy businesses from Dover to Apergy occurred on May 9, 2018; however, for ease of reference, and unless otherwise stated or the context otherwise requires, all references to “Apergy Corporation,” “Apergy,” “we,” “us” or “our” refer (i) prior to the Separation, to the Apergy businesses, consisting of entities, assets and liabilities conducting the upstream oil and gas business within Dover’s Energy segment and (ii) after the Separation, to Apergy Corporation and its consolidated subsidiaries. Interim Financial Information The accompanying unaudited condensed consolidated financial statements of Apergy have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and pursuant to the rules and regulations of the SEC pertaining to interim financial information. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP have been condensed or omitted. Therefore, these financial statements should be read in conjunction with the audited combined financial statements, and notes thereto, in the Information Statement included in Amendment No. 1 to the Form 10 filed with the SEC on April 12, 2018. The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Although these estimates are based on management’s best knowledge of current events and actions that we may undertake in the future, actual results may differ from our estimates. In the opinion of management, the accompanying unaudited condensed consolidated financial statements reflect all adjustments (consisting of normal recurring adjustments unless otherwise specified) necessary for a fair statement of our financial condition and results of operations as of and for the periods presented. Revenue, expenses, assets and liabilities can vary during each quarter of the year. Therefore, the results and trends in these financial statements may not be representative of the results that may be expected for the year ending December 31, 2018. Reclassifications Beginning in the first quarter of 2018, we changed our presentation of expenditures related to purchases of leased assets. Previously, these amounts were reported in the operating section of our cash flow statement as “other” in adjustments to reconcile net income but are now reported as changes in our operating assets and liabilities in the operating section of our cash flow statement as “leased assets and other.” During the first quarter of 2018, we changed our presentation of amortization expense primarily related to customer intangible assets. For the three and nine months ended September 30, 2017, we reclassified $11.0 million and $32.1 million of amortization expense previously reported as a component of “selling, general and administrative expense” to “cost of goods and services” on our condensed combined statements of income. During the second quarter of 2018, we changed our presentation of capital lease obligations. As of December 31, 2017, we reclassified $3.7 million of capital lease obligations previously reported as “other long-term liabilities” to “long-term debt” on our condensed combined balance sheet. Certain prior-year amounts have been reclassified to conform to the current year presentation. See Note 2 — New Accounting Standards for additional information.	1. Basis of Presentation On December 7, 2017, Dover (“Dover” or “Parent”) announced that its Board of Directors had approved a plan to spin-off spin-off, The accompanying Combined Financial Statements have been prepared on a stand-alone basis and are derived from Dover’s consolidated financial statements and accounting records. The Combined Financial Statements represent Apergy’s financial position, results of operations and cash flows as its business was operated as part of Dover prior to the distribution, in conformity with U.S. generally accepted accounting principles. All intercompany transactions between the Apergy entities have been eliminated. Transactions between Apergy and Dover, with the exception of transactions discussed in Note 3, are reflected in equity in the combined balance sheet as “Parent Company investment in Apergy” and in the combined statement of cash flows as a financing activity in “Net transfers (to) from Parent Company.” See Note 3 — Related Party Transactions for additional information regarding related party transactions. No portion of Dover’s third-party debt was historically held by an Apergy entity or is transferring to Apergy; therefore, no amount was included in the Combined Balance Sheets at December 31, 2017 and December 31, 2016. Accordingly, no interest expense related to third-party debt was recorded in the Combined Statements of Income. Intercompany notes payable to Dover of $224.5 million and $233.1 million at December 31, 2017 and 2016, respectively are classified within Parent Company investment in Apergy because the notes are not expected to be settled in cash. Accordingly, no interest expense was recorded in the Combined Statements of Income.

New Accounting Standards

New Accounting Standards	9 Months Ended
	Sep. 30, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Standards	NOTE 2 — NEW ACCOUNTING STANDARDS Recently Adopted Accounting Standards Effective January 1, 2018, we early adopted Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) No. 2018-02, “ Income Statement — Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. Effective January 1, 2018, we adopted ASU 2017-07, Compensation — Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. non-operating non-operating Effective January 1, 2018, we adopted ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business Effective January 1, 2018, we adopted ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments.” Effective January 1, 2018, we adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606). During the second half of 2015, Dover developed a project plan to implement ASU 2014-09, We have applied the following practical expedients or elections under the new standard: • We elected to omit disclosure of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less and (ii) contracts for which we recognize revenue at the amount to which we have the right to invoice for services performed. • We applied the practical expedient to not capitalize costs to obtain contracts with a duration of one year or less, which are expensed and included within “cost of goods and services” in the condensed consolidated statements of income. • We elected to use the practical expedient to not adjust the promised amount of consideration for the effects of a significant financing component if it is expected, at contract inception, that the period between when we transfer a promised good or service to a customer, and when the customer pays for that good or service, will be one year or less. Thus, we may not consider an advance payment to be a significant financing component, if it is received less than one year before product completion. • We elected to exclude all taxes assessed by a governmental authority that are both imposed on and concurrent with a specific revenue-producing transaction and collected from a customer (e.g., sales, use, value added, and some excise taxes) from the determination of the transaction price. As a result, our accounting policy of reporting revenue net of these taxes was not changed under the new standard. • We elected to account for shipping and handling activities performed after control of a good has been transferred to the customer as a contract fulfillment cost. As a result, our accounting policy related to shipping and handling was not changed under the new standard. See Note 11 — Revenue for additional information. Recently Issued Accounting Standards In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) right-of-use catch-up After the Separation from Dover, we developed a project plan and established a cross-functional team to continue the process of implementing the new guidance, which included an evaluation of the work performed by Dover prior to the Separation. We made progress on our plan including gathering information on all leases, surveying our businesses, assessing our portolfio of leases and compiling a central repository of active leases. During the third quarter of 2018, we completed diagnostic reviews of certain sampled leases to support our policy elections. Additionally, we made significant progress configuring and implementing a new lease software system. We continue to evaluate our policy elections and considerations under the new lease guidance, including the potential use of practical expedients, and we are in the process of updating our internal control and business processes. As we continue to assess the impact the guidance will have on our financial statements and related disclosures, internal control over financial reporting and other business practices and processes, we expect to recognize right of use assets and liabilities for operating leases in our consolidated balance sheet upon adoption. In June 2016, the FASB issued ASU 2016-13, “ Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use 350-40): internal-use internal-use

Related Party Transactions

Related Party Transactions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	NOTE 3 — RELATED PARTY TRANSACTIONS Dover Corporation Prior to the Separation, Dover provided certain services including corporate executive management, human resources, information technology, facilities, tax, shared services, finance and legal services. Dover continues to provide us certain of these services on a temporary basis following the Separation under a transition services agreement. Under the transition services agreement, Apergy pays a fee to Dover for services utilized under the transition services agreement, which fee is generally intended to allow Dover to recover all of its direct and indirect costs generally without profit. Except as provided otherwise in the transition services agreement, or with respect to specific services with other specified terms, the initial term of the transition services agreement will end on January 31, 2019, and the term may then be extended until May 9, 2019, or such other period set forth on the schedules thereto (subject to earlier termination under certain circumstances). All financial information presented prior to the Separation does not include all the expenses that would have been incurred had Apergy been a stand-alone public company. The corporate expenses allocated by Dover to these financial statements were $4.7 million for the three months ended September 30, 2017, and $7.4 million and $16.5 million for the nine months ended September 30, 2018 and 2017, respectively, which were recorded in “selling, general and administrative expense” in the condensed consolidated statements of income. For periods prior to the Separation, transactions between Apergy and Dover, with the exception of transactions discussed below with Dover’s affiliates, are reflected in “net parent investment in Apergy” in the condensed combined balance sheet as of December 31, 2017, and in “distributions to Dover Corporation, net” in the statements of cash flows for the nine months ended September 30, 2018 and 2017, as a financing activity. Accounts receivable, accounts payable and revenues with Dover and its affiliates were not material for the periods presented. We recognized royalty expense of $2.5 million for the three months ended September 30, 2017, and $2.3 million and $7.4 million for the nine months ended September 30, 2018 and 2017, respectively, related to the use of Dover’s intellectual property and patents which was included in “other expense, net” in the condensed consolidated statements of income. On April 1, 2018, patents and other intangibles owned by Dover related to our operations transferred to Apergy, and consequently, Apergy will no longer incur royalty charges related to these assets from Dover. Noncontrolling Interest For the nine months ended September 30, 2018 and 2017, we declared and paid $2.7 million and $1.2 million, respectively, of distributions to the noncontrolling interest holder in Norris Production Solutions Middle East LLC, a subsidiary in the Sultanate of Oman. We have a commission arrangement with our noncontrolling interest for 5% of certain annual product sales.	3. Related Party Transactions Dover provides Apergy certain services, which include corporate executive management, human resources, information technology, facilities, tax, shared services, finance and legal services. Some of these services will continue to be provided to Apergy on a temporary basis following the distribution. The financial information in these Combined Financial Statements does not necessarily include all the expenses that would have been incurred had Apergy been a separate, stand-alone entity. As such, the financial information herein may not necessarily reflect the combined financial position, results of operations, and cash flows of Apergy in the future or what they would have been had Apergy been a separate, stand-alone entity during the periods presented. Management believes that the methods used to allocate expenses to Apergy are reasonable. The corporate expenses allocated to Apergy totaled $22,987, $19,459 and $20,852 for the years ended December 31, 2017, 2016 and 2015, respectively, which are recorded in selling, general and administrative expenses in the Combined Statements of Income. As a stand-alone public company, Apergy’s total costs related to such support functions may differ from the costs that were historically allocated to it from Dover. Transactions between Apergy and Dover, with the exception of transactions discussed below with Dover’s affiliates, are reflected in equity in the Combined Balance Sheets as Parent Company investment in Apergy and in the Combined Statements of Cash Flows as a financing activity in Net transfers (to) from Parent Company. At December 31, 2017 and 2016, the Company’s outstanding accounts receivable and accounts payable balances with Dover and its affiliates were insignificant. These balances are included in receivables and accounts payable, respectively, on the Combined Balance Sheets. Intercompany revenues recorded from other Dover companies in the years ended December 31, 2017, 2016 and 2015, respectively, were insignificant. The Company recorded royalty expense related to Apergy’s use of Dover’s intellectual property and patents amounting to $9.8 million, $7.4 million and $10.4 million in 2017, 2016 and 2015, respectively, included within Other expense, net in the Combined Statements of Income. Patents and intangibles owned by Dover related to Apergy will transfer to Apergy upon separation. Upon separation, no further royalty charges are expected to be incurred by Apergy from Dover. Additionally, in 2016 and 2015, Apergy purchased certain patents and copyrights from Dover company for $3.7 million and $10.0 million, respectively. The patents and copyrights are included in Apergy’s intangibles balance and are being amortized. The Company paid $1.2 million and $1.7 million in 2017 and 2016, respectively, for distributions declared to its noncontrolling interest holder in Norris Production Solutions Middle East LLC, a subsidiary company in the Sultanate of Oman and is included within the Combined Statement of Stockholders’ Equity. The Company has a commission arrangement with its noncontrolling interest holder, for 5% of certain annual product sales. The commissions paid during 2017, 2016 and 2015, respectively, were not significant.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Earnings Per Share	NOTE 4 — EARNINGS PER SHARE On May 9, 2018, 77,339,828 shares of our common stock were distributed to Dover stockholders in conjunction with the Separation. See Note 1 — Basis Of Presentation And Separation for additional information. For comparative purposes, and to provide a more meaningful calculation of weighted-average shares outstanding, we have assumed the shares issued in conjunction with the Separation to be outstanding as of the beginning of each period prior to the Separation. In addition, we have assumed the potential dilutive securities outstanding as of May 8, 2018, were outstanding and fully dilutive in each of the periods prior to the Separation. A reconciliation of the number of shares used for the basic and diluted earnings per share calculation was as follows: Three Months Ended Nine Months Ended (in thousands, except per share data) 2018 2017 2018 2017 Net income attributable to Apergy $ 25,263 $ 18,421 $ 71,989 $ 50,444 Weighted-average number of shares outstanding 77,340 77,340 77,340 77,340 Dilutive effect of stock-based compensation 229 550 402 550 Total shares and dilutive securities 77,569 77,890 77,742 77,890 Basic earnings per share attributable to Apergy $ 0.33 $ 0.24 $ 0.93 $ 0.65 Diluted earnings per share attributable to Apergy $ 0.33 $ 0.24 $ 0.93 $ 0.65

Inventories

Inventories	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Inventory, Net [Abstract]
Inventories	NOTE 5 — INVENTORIES Inventories consisted of the following: (in thousands) September 30, December 31, Raw materials $ 48,735 $ 45,408 Work in progress 11,130 10,879 Finished goods 184,871 167,416 244,736 223,703 LIFO and valuation adjustments (25,603 ) (22,112 ) Inventories, net $ 219,133 $ 201,591	5. Inventories The components of inventories were as follows: December 31, December 31, Raw materials $ 45,408 $ 45,209 Work in progress 10,879 10,321 Finished goods 167,416 153,040 Subtotal 223,703 208,570 Less reserves (22,112 ) (24,012 ) Total $ 201,591 $ 184,558 At December 31, 2017 and 2016, approximately 28% and 32%, respectively, of the Company’s total inventories were accounted for using the LIFO method.

Property, Plant and Equipment

Property, Plant and Equipment	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	NOTE 6 — PROPERTY, PLANT AND EQUIPMENT Property, plant and equipment consisted of the following: (in thousands) September 30, December 31, Land $ 13,623 $ 13,557 Buildings and improvements 104,026 99,233 Machinery, equipment and other 501,148 446,261 618,797 559,051 Accumulated depreciation (382,730 ) (347,219 ) Property, plant and equipment, net $ 236,067 $ 211,832 During the nine months ended September 30, 2018, we transferred $42.5 million of inventory to property, plant and equipment related to certain assets entering our lease program.	6. Property, Plant and Equipment, net The components of property, plant and equipment, net were as follows: December 31, December 31, Land $ 13,557 $ 14,636 Buildings and improvements 99,233 91,927 Machinery, equipment and other 446,261 396,505 Property, plant and equipment, gross 559,051 503,068 Total accumulated depreciation (347,219 ) (301,321 ) Property, plant and equipment, net $ 211,832 $ 201,747 Total depreciation expense was $58,178, $56,068 and $60,831 for the years ended December 31, 2017, 2016 and 2015, respectively.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	NOTE 7 — GOODWILL AND INTANGIBLE ASSETS Goodwill The carrying amount, including changes therein, of goodwill by reporting segment was as follows: (in thousands) Production & Drilling Total December 31, 2017 $ 808,952 $ 101,136 $ 910,088 Purchase price adjustment * (53 ) — (53 ) Foreign currency translation (3,269 ) — (3,269 ) September 30, 2018 $ 805,630 $ 101,136 $ 906,766 * Purchase price adjustment related to our 2017 acquisition of PCP Oil Tools S.A. and Ener Tools S.A. Intangible Assets The components of our definite- and indefinite-lived intangible assets were as follows: September 30, 2018 December 31, 2017 (in thousands) Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Definite-lived intangible assets: Customer intangibles $ 569,832 $ 309,355 $ 260,477 $ 572,415 $ 276,655 $ 295,760 Trademarks 36,307 20,648 15,659 36,312 17,821 18,491 Patents 38,514 22,959 15,555 38,679 20,449 18,230 Unpatented technologies 9,700 9,700 — 9,700 9,700 — Drawings and manuals 3,047 2,163 884 3,067 2,109 958 Other 5,346 4,124 1,222 5,382 3,911 1,471 662,746 368,949 293,797 665,555 330,645 334,910 Indefinite-lived intangible assets: Trademarks 3,600 — 3,600 3,600 — 3,600 Total $ 666,346 $ 368,949 $ 297,397 $ 669,155 $ 330,645 $ 338,510	7. Goodwill and Other Intangible Assets Goodwill The changes in the carrying value of goodwill by operating segment were as follows: Production & Drilling Total Balance at December 31, 2015 $ 800,792 $ 101,136 $ 901,928 Foreign currency translation 651 — 651 Balance at December 31, 2016 801,443 101,136 902,579 Acquisitions 5,053 — 5,053 Foreign currency translation 2,456 — 2,456 Balance at December 31, 2017 $ 808,952 $ 101,136 $ 910,088 Annual impairment testing Historically, the Company was part of the Dover Energy operating segment. The Company performed its annual goodwill impairment test for its two historical reporting units (i) Drilling and Production, excluding a business component that will be retained by Dover (“D&P”) and (ii) Dover Energy Automation (“DEA”), and found no impairment. For both reporting units, based upon the annual goodwill analyses performed by the Company as of October 1, 2017 and 2016, the fair values exceeded the carrying values, and no impairment was required. Beginning in the fourth quarter of 2017, the Company also performed its annual goodwill impairment testing based upon the new segment structure discussed in Note 16 — Segment Information. The Company performed goodwill impairment testing on its two new reporting units as of October 1, 2017: (i) Production & Automation Technologies (“P&AT”) and (ii) Drilling Technologies (“DT”). For both reporting units, the fair values were substantially in excess of carrying values and no impairment was required. The annual impairment test is performed using a discounted cash flow analysis as discussed in Note 2 — Summary of Significant Accounting Policies. The Company performed a quantitative goodwill impairment test for each of its reporting units, concluding that the fair values were in excess of their carrying values. As previously noted, the fair values of each of the Company’s reporting units were determined using a discounted cash flow analysis which included management’s assumptions as to future cash flows and long-term growth rates as of the date of the impairment test. The discount rates used in these analyses were based on a capital asset pricing model and published relevant industry rates. The Company used discount rates related to that historical period commensurate with the risks and uncertainties inherent to each reporting unit and in management’s internally developed forecasts. Discount rates used in the Company’s 2017 and 2016 valuations were 10.0% and 10.5%, respectively. As of October 1, 2017, the goodwill balances for the D&P and DEA reporting units were $733,641 and $172,480, respectively. The D&P and DEA reporting units had fair values in excess of their carrying values of 90% and 233%, respectively. Under the new segment structure, as of October 1, 2017, the goodwill balances for the P&AT and DT reporting units were $804,985 and $101,136, respectively. The P&AT and DT reporting units had fair values in excess of their carrying values of 69% and 464%, respectively. While the Company believes the assumptions used in the 2017 and 2016 impairment analyses are reasonable and representative of expected results, if market conditions worsen over an extended period of time, an impairment of goodwill or assets may occur. The Company will continue to monitor the long-term outlook and forecasts, including estimated future cash flows, for these businesses and the impact on the carrying value of goodwill and assets. Intangible Assets The following table provides the gross carrying value and accumulated amortization for each major class of intangible assets: December 31, 2017 December 31, 2016 Gross Amount Accumulated Amortization Net Gross Amount Accumulated Amortization Net Amortized intangible assets: Customer Intangibles $ 572,415 $ 276,655 $ 295,760 $ 566,602 $ 229,902 $ 336,700 Trademarks 36,312 17,821 18,491 36,296 14,013 22,283 Patents 38,679 20,449 18,230 38,106 16,662 21,444 Unpatented Technologies 9,700 9,700 — 9,700 9,700 — Drawings & Manuals 3,067 2,109 958 3,001 1,942 1,059 Other 5,382 3,911 1,471 5,270 3,539 1,731 Total amortized intangibles 665,555 330,645 334,910 658,975 275,758 383,217 Unamortized intangible assets: Trademarks 3,600 — 3,600 3,600 — 3,600 Total intangible assets $ 669,155 $ 330,645 $ 338,510 $ 662,575 $ 275,758 $ 386,817 The Company recorded $4,538 of acquired intangible assets in 2017. See Note 4 — Acquisitions. Total amortization related to the Company’s intangible assets was $53,701, $55,987 and $59,161 for the years ended December 31, 2017, 2016 and 2015, respectively. Estimated future amortization expense related to intangible assets held at December 31, 2017 is as follows: Estimated 2018 $ 52,357 2019 51,509 2020 50,059 2021 49,231 2022 47,683

Debt

Debt	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt	NOTE 8 — DEBT Long-term debt consisted of the following: (in thousands) September 30, December 31, Revolving credit facility $ — $ — Term loan facility 395,000 — 6.375% Senior Notes due 2026 300,000 — Capital leases 4,337 3,742 Total 699,337 3,742 Net unamortized discounts and issuance costs (11,794 ) — Total long-term debt $ 687,543 $ 3,742 Senior Notes On May 3, 2018, and in connection with the Separation, we completed the private placement of $300 million in aggregate principal amount of 6.375% senior notes due May 2026 (“Senior Notes”). Interest on the Senior Notes is payable semi-annually in arrears on May 1 and November 1 of each year, commencing on November 1, 2018. Net proceeds of $293.8 million from the offering were utilized to partially fund the $700 million cash payment to Dover at the Separation and to pay fees and expenses incurred in connection with the Separation. The terms of the Senior Notes are governed by the indenture dated as of May 3, 2018, between Apergy and Wells Fargo Bank, N.A., as trustee, and are guaranteed, on a senior unsecured basis, by the subsidiary guarantors of our senior secured credit facilities as described below. At any time prior to May 1, 2021, we may redeem all or part of the Senior Notes at a redemption price equal to 100% of the principal amount of the Senior Notes redeemed plus a premium, as defined in the indenture, plus accrued and unpaid interest. Beginning on or after May 1, 2021, we may redeem the Senior Notes, in whole or in part, at certain tiered redemption prices as defined in the indenture, plus accrued and unpaid interest. The Senior Notes are our senior unsecured obligations. The Senior Notes rank equally in right of payment with our future and existing senior debt but are effectively subordinated to our future and existing debt to the extent of the assets securing such senior debt. The Senior Notes rank senior in right of payment to all of our future subordinated debt. In connection with the private placement, we granted the initial purchasers of the Senior Notes certain registration rights under a registration right agreement. We have agreed for the benefit of the holders of the Senior Notes to use our commercially reasonable efforts to file and cause to be effective a registration statement with the SEC relating to a registered offer to exchange the Senior Notes for an issue of SEC-registered Senior Secured Credit Facilities On May 9, 2018, Apergy entered into a new credit agreement (“credit agreement”) governing the terms of its new senior secured credit facilities, consisting of (i) a seven-year senior secured term loan B facility (“term loan facility”) and (ii) a five-year senior secured revolving credit facility (“revolving credit facility,” and together with the term loan facility, the “senior secured credit facilities”), with JPMorgan Chase Bank, N.A. as administrative agent. The net proceeds of the senior secured credit facilities were used (i) to pay fees and expenses in connection with the Separation, (ii) partially fund the cash payment to Dover and (iii) provide for working capital and other general corporate purposes. The senior secured credit facilities are jointly and severally guaranteed by Apergy and certain of Apergy’s wholly owned U.S. subsidiaries (“guarantors”), on a senior secured basis, and are secured by substantially all tangible and intangible assets of Apergy and the guarantors, except for certain excluded assets. At our election, outstanding borrowings under the senior secured credit facilities will accrue interest at a per annum rate of (i) LIBOR plus a margin or (ii) a base rate plus a margin. The senior secured credit facilities contain a number of customary covenants that, among other things, will limit or restrict the ability of Apergy and the restricted subsidiaries to, subject to certain qualifications and exceptions, perform certain activities which include, but are not limited to (i) incur additional indebtedness, (ii) make acquisitions and (iii) pay dividends or other payments in respect of our capital stock. Additionally, Apergy will be required to maintain (a) a minimum interest coverage ratio, as defined in the credit agreement, of 2.75 to 1.00 and (b) a maximum total leverage ratio, as defined in the credit agreement, of 4.00 to 1.00 through the fiscal quarter ending June 30, 2019, then 3.75 to 1.00 through the fiscal quarter ending June 30, 2020, then 3.50 to 1.00 thereafter. Term Loan Facility. re-borrowed. The term loan is subject to mandatory amortization payments of 1.0% per annum of the initial commitment of $415 million paid quarterly. Additionally, subject to certain exceptions, the term loan facility is subject to mandatory prepayments, including the amount equal to: 100% of the net cash proceeds of all non-ordinary Revolving Credit Facility. re-borrowed.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss)	NOTE 9 — ACCUMULATED OTHER COMPREHENSIVE LOSS Accumulated other comprehensive loss consisted of the following: (in thousands) Foreign Currency Defined Pension and Accumulated Other December 31, 2017 $ (21,935 ) $ (4,480 ) $ (26,415 ) Reclassification adjustment for cumulative effect of change in accounting principle — (1,315 ) (1,315 ) Net transfer from Dover Corporation — (2,421 ) (2,421 ) Other comprehensive income (loss) before reclassifications, net of tax (9,080 ) 170 (8,910 ) Reclassification adjustment for net losses (gains) included in net income, net of tax — 534 534 Other comprehensive income (loss), (9,080 ) 704 (8,376 ) September 30, 2018 $ (31,015 ) $ (7,512 ) $ (38,527 ) Reclassification adjustments from accumulated other comprehensive loss to net income related to defined pension and other post-retirement benefits consisted of the following: Three Months Ended Nine Months Ended Affected line items on the (in thousands) 2018 2017 2018 2017 Amortization of actuarial loss (1) $ 116 $ 100 $ 243 $ 299 Other expense, net Settlement loss (1) 484 — 484 — Selling, general and administrative expense Total before tax 600 100 727 299 Income before income taxes Tax benefit (161 ) (35 ) (192 ) (102 ) Provision for income taxes $439 $65 $535 $197 Net income (1) These accumulated comprehensive loss components are included in the computation of net periodic benefit cost (See Note16—Employee Benefit Plans for additional information).	15. Other Comprehensive Income (Loss) The amounts recognized in Other comprehensive income (loss) were as follows: Year Ended December 31, 2017 Pre-tax Tax Net of tax Foreign currency translation adjustments $ 4,358 $ — $ 4,358 Pension and other post-retirement benefit plans 3,827 (971 ) 2,856 Total other comprehensive income (loss) $ 8,185 $ (971 ) $ 7,214 Year Ended December 31, 2016 Pre-tax Tax Net of tax Foreign currency translation adjustments $ 953 $ — $ 953 Pension and other post-retirement benefit plans 154 (42 ) 112 Total other comprehensive income (loss) $ 1,107 $ (42 ) $ 1,065 Year Ended December 31, 2015 Pre-tax Tax Net of tax Foreign currency translation adjustments $ (11,691 ) $ — $ (11,691 ) Pension and other post-retirement benefit plans (393 ) 124 (269 ) Total other comprehensive (loss) income $ (12,084 ) $ 124 $ (11,960 ) The components of Accumulated other comprehensive (loss) income are as follows: December 31, December 31, Cumulative foreign currency translation adjustments $ (21,935 ) $ (26,293 ) Pension and other post-retirement benefit plans (4,480 ) (7,336 ) $ (26,415 ) $ (33,629 ) Total Comprehensive income (loss) were as follows: Years Ended December 31, 2017 2016 2015 Net income (loss) attributable to Apergy $ 110,638 $ (12,642 ) $ 51,698 Other comprehensive income (loss) 7,214 1,065 (11,960 ) Comprehensive income (loss) $ 117,852 $ (11,577 ) $ 39,738 Amounts reclassified from Accumulated other comprehensive income (loss) to income (loss) during the year ended December 31, 2017, 2016 and 2015 were as follows: Years Ended December 31, 2017 2016 2015 Pension and other post-retirement benefit plans: Amortization of actuarial losses and net transition obligation $ 397 $ 362 $ 340 Amortization of prior service costs 2 2 2 Total before tax 399 364 342 Tax benefit (141 ) (129 ) (120 ) Net of tax $ 258 $ 235 $ 222 The Company recognizes net periodic benefit cost, which includes amortization of net actuarial losses and prior service costs, in both Selling, general and administrative expenses and Cost of goods and services in the Combined Statements of Income, depending on the functional area of the underlying employees included in the plans.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	NOTE 10 — COMMITMENTS AND CONTINGENCIES Guarantees and Indemnifications We have provided indemnities in connection with sales of certain businesses and assets, including representations and warranties, covenants and related indemnities for environmental health and safety, tax and employment matters. We do not have any material liabilities recorded for these indemnifications and are not aware of any claims or other information that would give rise to material payments under such indemnities. In connection with the Separation, we entered into agreements with Dover that govern the treatment between Dover and us of certain indemnification matters and litigation responsibility. Generally, the separation and distribution agreement provides for cross-indemnities principally designed to place financial responsibility for the obligations and liabilities of our business with us and to place financial responsibility for the obligations and liabilities of Dover’s business with Dover. The separation and distribution agreement also establishes procedures for handling claims subject to indemnification and related matters. In addition, pursuant to the tax matters agreement, we have agreed to indemnify Dover and its affiliates against any and all tax-related liabilities incurred by them relating to the Separation and/or certain related transactions to the extent caused by an acquisition of Apergy stock or assets or by any other action or failure to act undertaken by Apergy or its affiliates. As of September 30, 2018 and December 31, 2017, we had $5.5 million and $8.1 million, respectively, of outstanding letters of credit, surety bonds and guarantees which expire at various dates through 2020. These financial instruments are primarily maintained as security for insurance, warranty and other performance obligations. Generally, we would only be liable for the amount of these letters of credit in the event of default in the performance of our obligations, the probability of which we believe is remote. Litigation We are a party to a number of legal proceedings incidental to our businesses. These proceedings primarily involve claims by private parties alleging injury arising out of use of our products, patent infringement, employment matters, and commercial disputes. Management and legal counsel review the probable outcome of such proceedings, the costs and expenses reasonably expected to be incurred and currently accrued to-date,	13. Commitments and Contingent Liabilities Lease Commitments The Company leases certain facilities and equipment under operating leases, many of which contain renewal options. Total rental expense, net of insignificant sublease rental income, for all operating leases was $16,837, $17,936 and $16,992 for the years ended December 31, 2017, 2016 and 2015, respectively. Contingent rentals under the operating leases were not significant. The aggregate future minimum lease payments for operating and capital leases as of December 31, 2017 are as follows: Operating Capital 2018 $ 11,668 $ 2,232 2019 10,646 1,696 2020 7,639 181 2021 5,309 — 2022 4,625 — Thereafter 5,105 — Total $ 44,992 $ 4,109 Guarantees The Company has provided indemnities in connection with sales of certain businesses and assets, including representations and warranties and related indemnities for environmental, health and safety, tax and employment matters. The Company does not have any material liabilities recorded for these indemnifications and is not aware of any claims or other information that would give rise to material payments under such indemnities. Letters of Credit As of December 31, 2017 and 2016, the Company had approximately $8,100 and $16,045 outstanding in letters of credit and guarantees with financial institutions, which expire at various dates in 2018 through 2020. These letters of credit are primarily maintained as security for insurance, warranty and other performance obligations. In general, the Company would only be liable for the amount of these letters of credit in the event of default in the performance of the Company’s obligations, the probability of which we believe is remote. Litigation The Company’s environmental matters that are probable and estimable were insignificant at December 31, 2017 and 2016. The environmental matters relate to ongoing remedial activities performed in cooperation with regulatory authorities. The Company and certain of its subsidiaries are also parties to a number of other legal proceedings incidental to their businesses. These proceedings primarily involve claims by private parties alleging injury arising out of use of the Company’s products, patent infringement, employment matters and commercial disputes. Management and legal counsel, at least quarterly, review the probable outcome of such proceedings, the costs and expenses reasonably expected to be incurred and currently accrued to-date. The Company has reserves for other legal matters that are probable and estimable, and at December 31, 2017 and 2016, these reserves were not significant. While it is not possible at this time to predict the outcome of these legal actions, in the opinion of management, based on the aforementioned reviews, the Company is not currently involved in any legal proceedings which, individually or in the aggregate, could have a material effect on its financial position, results of operations, or cash flows.

Revenue

Revenue	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue	NOTE 11 — REVENUE Our revenue is substantially generated from product sales. For the nine months ended September 30, 2018, approximately 89% of our revenue was generated from product sales. Our remaining revenue was derived from services, leases and other, which represented approximately 7%, 3%, and 1%, respectively, of total revenue for the nine months ended September 30, 2018. Product revenue is derived from the sale of drilling and production equipment. Service revenue is earned as technical advisory assistance and field services related to our products are provided. Lease revenue is derived from month-to-month The majority of our revenue is short cycle in nature, with shipments occurring within a year from the customer order date. A small portion of our revenue is derived from contracts extending over one year. Our payment terms generally range between 30 to 90 days and vary by the location of our businesses and the types and volumes of products manufactured and sold, among other factors. Costs incurred to obtain a customer contract are generally not material to us. Disaggregation of Revenue Revenue disaggregated by end market in each of our reporting segments was as follows: (in thousands) Three Months Ended Nine Months Drilling Technologies $ 75,254 $ 209,727 Production & Automation Technologies: Artificial lift 188,005 544,566 Digital products 31,114 85,347 Other production equipment 22,380 68,922 Intra-segment eliminations (285 ) (2,244 ) 241,214 696,591 Total revenue $ 316,468 $ 906,318 Revenue disaggregated by geography was as follows: (in thousands) Three Months Ended Nine Months Ended United States $ 252,747 $ 713,373 Canada 20,759 58,639 Middle East 13,645 40,091 Europe 7,625 27,805 Latin America 8,364 25,097 Asia-Pacific 3,715 13,900 Other 9,613 27,413 Total revenue $ 316,468 $ 906,318 Performance Obligations The majority of our contracts have a single performance obligation which represents, in most cases, the equipment or product sold to the customer. Some contracts include multiple performance obligations such as a product and the related installation, extended warranty and/or maintenance services. For contracts with multiple performance obligations, we allocate the transaction price to each performance obligation based on the estimated relative standalone selling prices of the promised goods or services underlying each performance obligation. We typically use observable prices to determine the stand-alone selling price of a performance obligation and utilize a cost plus margin approach when observable prices are not available. Substantially all of our performance obligations are recognized at a point in time and are primarily related to our product revenue derived from the sale of drilling and production equipment. Revenue is recognized when control transfers to the customer upon shipment or completion of installation, testing, certification, or other substantive acceptance provisions required under the contract. Revenue is recognized over time for our service and lease offerings. Service revenue is recognized over time as we provide technical advisory assistance and field services related to our products. Warranties The majority of our contracts contain standard warranties in connection with the sale of a product to a customer which provide a customer assurance that the related product will function for a period of time as the parties intended. In addition to our standard warranties, we also offer extended warranties to our customers. Warranties provided as part of our product offerings are analyzed to determine whether they represent a distinct service, and if so, are recognized as service revenue over the related warranty period. Remaining performance obligations As of September 30, 2018, we did not have any contracts with an original length of greater than a year, from which revenue is expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied). Contract balances Contract assets and contract liabilities from contracts with customers were as follows: (in thousands) September 30, 2018 January 1, 2018 Contract assets $ 3,475 $ 4,733 Contract liabilities — current 6,827 4,487 Contract assets primarily relate to our right to consideration for work completed but not billed at the reporting date and are recorded in “prepaid expenses and other current assets” on our condensed consolidated balance sheets. Contract assets are transferred to receivables when the right to consideration becomes unconditional. Contract liabilities relate to our obligation to transfer goods or services to a customer for which we have received advance consideration (or an amount of consideration is due) from the customer. Current contract liabilities are recorded in other “accrued expenses and other current liabilities” on our condensed consolidated balance sheets. Critical Accounting Estimates Estimates are used to determine the amount of variable consideration in contracts, the determination of the standalone selling price among separate performance obligations, as well as the determination of the measure of progress for contracts where revenue is recognized over time. Some contracts with customers include variable consideration primarily related to volume rebates. We estimate variable consideration at the most likely amount to determine the total consideration which we expect to be entitled. Estimated amounts are included in the transaction price to the extent it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is resolved. Our estimates of variable consideration and the determination of whether to include estimated amounts in the transaction price are largely based on an assessment of our anticipated performance and all information that is reasonably available.

Restructuring and Other Related

Restructuring and Other Related Charges	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Restructuring and Other Related Charges	NOTE 12 — RESTRUCTURING AND OTHER RELATED CHARGES Restructuring and other related charges as classified in our condensed consolidated statements of income were as follows: Three Months Ended Nine Months Ended (in thousands) 2018 2017 2018 2017 Cost of goods and services $ (33 ) $ (16 ) $ 1,557 $ (17 ) Selling, general and administrative expense (6 ) 24 916 38 Total $ (39 ) $ 8 $ 2,473 $ 21 Restructuring and other related charges during 2018 were incurred in our Production & Automation Technologies segment. These charges reflect costs associated with exiting certain product lines and include severance and related benefit costs, early lease termination and other related charges. Our restructuring programs were designed to better align our costs and operations with current market conditions and include measures such as targeted facility consolidations, headcount reductions and other actions to further optimize our operations. Our liability balances for restructuring and other exit activities were $1.5 million and $2.6 million as of September 30, 2018 and December 31, 2017, respectively, and primarily include ongoing lease commitment obligations for facilities closed in prior periods and employee severance and related benefits. Our restructuring initiatives are complete and our liability balances for restructuring and other exit activities are expected to be mostly settled by mid-2019.	9. Restructuring Activities The Company initiated various restructuring programs and incurred severance and other restructuring costs by segment as follows: Years Ended December 31, 2017 2016 2015 Production & Automation Technologies $ 6,921 $ 12,757 $ 18,750 Drilling Technologies — 2,405 2,480 Total $ 6,921 $ 15,162 $ 21,230 These amounts are classified in the Combined Statements of Income as follows: Cost of goods and services $ 6,332 $ 9,465 $ 9,095 Selling, general and administrative expenses 589 5,697 12,135 Total $ 6,921 $ 15,162 $ 21,230 The restructuring charges of $6,921, $15,162 and $21,230 incurred during 2017, 2016 and 2015, respectively, included the following programs, which were substantially completed during those three years: • The Production & Automation Technologies segment incurred restructuring charges of $6,921, $12,757 and $18,750 during 2017, 2016 and 2015, respectively, related to various programs across the segment, primarily focused on facility consolidations, exit of certain nonstrategic product lines and workforce reductions. The 2017 programs were initiated to continue to optimize our operations as the market recovered and the 2016 and 2015 programs were initiated to better align the cost base with the significantly lower demand environment. • The Drilling Technologies segment recorded no restructuring charges during 2017. The segment recorded $2,405 and $2,480 in restructuring charges during 2016 and 2015, respectively, related to various programs across the segment, primarily focused on workforce reductions across various businesses to better align the cost base with the significantly lower demand environment. The following table details the Company’s severance and other restructuring accrual activities: Severance Exit Total Balance at December 31, 2014 $ 95 $ — $ 95 Restructuring charges 9,366 11,864 21,230 Payments (8,197 ) (3,947 ) (12,144 ) Other, including foreign currency translation (1) (100 ) (7,194 ) (7,294 ) Balance at December 31, 2015 1,164 723 1,887 Restructuring charges 10,496 4,666 15,162 Payments (11,235 ) (2,410 ) (13,645 ) Other, including foreign currency translation (1) (175 ) (2,770 ) (2,945 ) Balance at December 31, 2016 $ 250 $ 209 $ 459 Restructuring charges 151 6,770 6,921 Payments (400 ) (978 ) (1,378 ) Other, including foreign currency translation (1) (1 ) (3,450 ) (3,451 ) Balance at December 31, 2017 $ — $ 2,551 $ 2,551 (1) Other activity in exit reserves primarily represents the non-cash write-off The restructuring accrual balance at December 31, 2017 primarily reflects restructuring plans initiated during the year, as well as ongoing lease commitment obligations for facilities closed in prior periods. Additional programs may be implemented during 2018 with related restructuring charges.

Income Taxes

Income Taxes	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	NOTE 13 — INCOME TAXES Prior to the Separation, our operations were historically included in Dover’s U.S. combined federal and state income tax returns. For the periods prior to the Separation, income tax expense and deferred tax balances are presented in these condensed consolidated financial statements as if Apergy filed its own tax returns in each jurisdiction and include tax losses and tax credits that may not reflect tax positions taken by Dover. In many cases, tax losses and tax credits generated by Apergy through the date of the Separation were utilized by Dover. Income tax payable balances as of December 31, 2017, were classified within “net parent investment in Apergy” on the condensed combined balance sheet since Dover is legally liable for the tax. Our income tax provision reflected effective tax rates of 23.2% and 30.6% for the three months ended September 30, 2018 and 2017, respectively, and 25.2% and 30.9% for the nine months ended September 30, 2018 and 2017, respectively. The year-over-year decrease in the effective tax rates was primarily due to the Tax Reform Act, which was enacted on December 22, 2017, and which reduced the U.S. corporate income tax rate from a maximum of 35% to 21%, effective January 1, 2018. This benefit was partially offset by tax on capital gains related to certain reorganizations of our subsidiaries as a result of the Separation. We recognized provisional tax impacts related to deemed repatriated earnings and the benefit for the revaluation of deferred tax assets and liabilities in our combined financial statements for the year ended December 31, 2017. The provisions in the Tax Reform Act are broad and complex. As of September 30, 2018, we have not yet completed our accounting for the income tax effects of the Tax Reform Act but have made reasonable estimates of those effects on our existing deferred income tax balances and the one-time	11. Income Taxes The operations of Apergy have been historically included in Dover’s U.S. combined federal and state income tax returns. Income tax expense and deferred tax balances are presented in these financial statements as if Apergy filed its own tax returns in each jurisdiction. These statements include tax losses and tax credits that may not reflect tax positions taken by Dover. In many cases, tax losses and tax credits generated by Apergy have been utilized by Dover. Income taxes have been based on the following components of income (loss) before income taxes in the Combined Statements of Income: Years Ended December 31, 2017 2016 2015 Domestic $ 66,852 $ (25,926 ) $ 61,670 Foreign 22,432 7,092 15,595 Total $ 89,284 $ (18,834 ) $ 77,265 Income tax (benefit) expense relating to continuing operations for the years ended December 31, 2017 and 2016 is comprised of the following: Years Ended December 31, 2017 2016 2015 Current: U.S. federal $ 42,312 $ 8,872 $ 40,415 State and local 4,230 1,995 (332 ) Foreign 6,176 971 5,344 Total current 52,718 11,838 45,427 Deferred: U.S. federal (73,544 ) (19,161 ) (23,135 ) State and local (1,361 ) (771 ) 4,141 Foreign (97 ) 51 (2,302 ) Total deferred (75,002 ) (19,881 ) (21,296 ) Total (benefit) expense $ (22,284 ) $ (8,043 ) $ 24,131 Differences between the effective income tax rate and the U.S. federal income statutory tax rate are as follows: Years Ended 2017 2016 2015 U.S. federal income tax rate 35.0 % 35.0 % 35.0 % State and local taxes, net of federal income tax benefit 2.1 (3.9 ) 3.1 Foreign operations tax effect (2.8 ) 7.8 (3.1 ) Research and experimentation tax credits (0.7 ) 2.3 (0.7 ) Domestic manufacturing deduction (4.5 ) 6.2 (4.6 ) Nondeductible expenses 0.7 (3.3 ) 1.0 ESOP dividends (0.2 ) 2.9 (0.7 ) Branch income 1.1 (2.9 ) 0.8 Changes due to the Tax Reform Act (55.2 ) — — Other (0.5 ) (1.4 ) 0.4 Effective tax rate from continuing operations (25.0 )% 42.7 % 31.2 % The tax effects of temporary differences that give rise to future deferred tax assets and liabilities are as follows: December 31, December 31, Deferred Tax Assets: Accrued compensation, principally post-retirement and other employee benefits $ 4,568 $ 9,126 Accrued expenses, principally for state income taxes, interest and warranty 846 1,512 Net operating loss and other carryforwards 1,280 1,082 Accounts receivable, principally due to allowance for doubtful accounts 827 1,780 Long-term liabilities, principally warranty, environmental and exit cost 678 620 Other assets 132 459 Total gross deferred tax assets 8,331 14,579 Valuation allowance (1,280 ) (1,082 ) Total deferred tax assets, net of valuation allowances $ 7,051 $ 13,497 Deferred Tax Liabilities: Inventories, principally due to reserves for financial reporting purposes and capitalization for tax purposes $ (3,687 ) $ (4,754 ) Intangible assets, principally due to different tax and financial reporting bases and amortization lives (83,669 ) (149,500 ) Property, plant and equipment, principally due to differences in depreciation (16,134 ) (26,254 ) Total gross deferred tax liabilities (103,490 ) (180,508 ) Net deferred tax liability $ (96,439 ) $ (167,011 ) Classified as follows in the Combined Balance Sheets: Other assets and deferred charges $ 546 $ 554 Deferred income taxes (96,985 ) (167,565 ) $ (96,439 ) $ (167,011 ) As of December 31, 2017, the Company had non-U.S. non-U.S. losses The Company maintains valuation allowances by jurisdiction against the deferred tax assets related to these carryforwards as utilization of these tax benefits is not assured for certain jurisdictions. The Tax Reform Act, which was enacted on December 22, 2017, permanently reduces the U.S. corporate income tax rate from a maximum of 35% to a flat 21% rate, effective January 1, 2018. As a result of the reduction in the U.S. corporate income tax rate, the Company revalued its ending net deferred tax liabilities as of December 31, 2017 and recognized a provisional tax benefit of $53.2 million. The Tax Reform Act also imposed a tax for a one-time non-U.S. The GILTI provisions of the Tax Reform Act require the Company to include in its U.S. income tax return foreign subsidiary earnings in excess of an allowable return on the foreign subsidiary’s tangible assets. The Company expects that it will be subject to incremental U.S. tax on GILTI income beginning in 2018, due to expense allocations required by the U.S. foreign tax credit rules. The Company has elected to account for GILTI tax in the period in which it is incurred, and therefore has not provided any deferred tax impacts of GILTI in its combined financial statements for the year ended December 31, 2017. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118 (“SAB 118”) to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Reform Act. In accordance with the SAB 118 guidance, the Company has recognized the provisional tax impacts related to deemed repatriated earnings and the benefit for the revaluation of deferred tax assets and liabilities in its combined financial statements for the year ended December 31, 2017. The final impact may differ from these provisional amounts, possibly materially, due to, among other things, issuance of additional regulatory guidance, changes in interpretations and assumptions the Company has made, and actions the Company may take as a result of the Tax Reform Act. In accordance with SAB 118 the financial reporting impact of the Tax Reform Act will be completed in the fourth quarter of 2018. The Company files U.S., federal, state, local and foreign tax returns. The Company is routinely audited by the tax authorities in these jurisdictions, and a number of audits are currently underway. The Company is no longer subject to examinations of its federal income tax returns for years through 2013. All significant state, local and international matters have been concluded for years through 2012. The Company believes that all income tax uncertainties have been properly accounted. The Company has not recorded a liability for uncertain tax positions at December 31, 2017 and 2016.

Fair Value Measurements

Fair Value Measurements	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	NOTE 14 — FAIR VALUE MEASUREMENTS We had no outstanding derivative contracts as of September 30, 2018 and December 31, 2017. Other assets and liabilities measured at fair value on a recurring basis as of September 30, 2018 and December 31, 2017, were not significant; thus, no fair value disclosures are presented. The fair value, based on Level 1 quoted market rates, of our Senior Notes was approximately $308.6 million at September 30, 2018, as compared to the $300 million face value of the debt. The fair value, based on Level 2 quoted market rates, of our term loan facility was approximately $397.0 million at September 30, 2018, as compared to the $395 million face value of the debt. The carrying amounts of cash and cash equivalents, trade receivables, accounts payable, as well as amounts included in other current assets and other current liabilities that meet the definition of financial instruments, approximate fair value due to their short-term nature. Credit Risk By their nature, financial instruments involve risk, including credit risk, for non-performance non-performance	10. Fair Value Measurements The Company had outstanding contracts as of December 31, 2017 and 2016 respectively, that were not designated as hedging instruments. These instruments are used to reduce the Company’s exposure for operating receivables and payables that are denominated in non-functional Fair Value Measurements Accounting Standards Codification (“ASC”) 820, “Fair Value Measurements and Disclosures,” establishes a hierarchy for measuring fair value. A financial instrument’s categorization within the hierarchy is based on the lowest level of input that is significant to the fair value measurement. ASC 820 establishes three levels of inputs that may be used to measure fair value as follows: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 inputs include inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices in active markets for similar assets and liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of assets or liabilities. Level 3 inputs are unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. The Company’s assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 and 2016 were not significant and no tabular disclosures are presented. In addition to fair value disclosure requirements related to financial instruments carried at fair value, accounting standards require disclosures regarding the fair value of all of the Company’s financial instruments. The carrying values of cash equivalents, trade receivables and accounts payable are reasonable estimates of their fair values as of December 31, 2017 and 2016 due to the short-term nature of these instruments.

Equity and Cash Incentive Progr

Equity and Cash Incentive Program	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Share Based Compensation Abstract
Equity and Cash Incentive Program	NOTE 15 — EQUITY AND CASH INCENTIVE PROGRAM Prior to the Separation, Dover granted share-based awards to its officers and other key employees, including certain Apergy individuals. All awards granted under the program consisted of Dover common shares and are not necessarily indicative of the results that Apergy would have experienced as a stand-alone public company for the periods presented prior to the Separation. Effective with the Separation, outstanding Dover share-based awards were converted to Apergy share-based awards, with the exception of outstanding Dover performance share awards that relate to performance periods ending after the Separation. Such performance share awards were cancelled effective with the Separation. In connection with the Separation, the Board of Directors of Apergy adopted the Apergy Corporation 2018 Equity and Cash Incentive Plan (“2018 Plan”). The 2018 Plan was also approved by Dover in its capacity as the sole stockholder of Apergy at the time of adoption. A total of 6.5 million shares of common stock are reserved for issuance under the 2018 Plan, subject to customary adjustments arising from stock splits and other similar changes. The 2018 Plan authorized the grant of stock options, stock-settled stock appreciation rights (“SARs”), restricted stock awards, restricted stock units, performance share awards, cash performance awards, directors’ shares and deferred stock units. The Apergy Compensation Committee determines the exercise price for options and the base price of SARs, which may not be less than the fair market value of Apergy common stock on the date of grant. Generally, stock options or SARs vest after three years of service and expire at the end of ten years. Performance share awards vest if Apergy achieves certain pre-established In May 2018 and in connection with the Separation, 352 thousand restricted stock awards and 87 thousand performance shares were granted to employees. Stock-based compensation expense is reported within “selling, general and administrative expense” in the condensed consolidated statements of income. Stock-based compensation expense relating to all stock-based incentive plans was as follows: Three Months Ended Nine Months Ended 2018 2017 2018 2017 Stock-based compensation expense $ 1,768 $ 630 $ 3,129 $ 1,762 Tax benefit (421 ) (219 ) (717 ) (611 ) Stock-based compensation expense, net of tax $ 1,347 $ 411 $ 2,412 $ 1,151	12. Equity and Cash Incentive Program Dover grants share-based awards to its officers and other key employees, including certain Apergy individuals. The following disclosures reflect the portion of Dover’s program in which Apergy employees participate. All awards granted under the program consist of Dover common shares and are not necessarily indicative of the results that Apergy would have experienced as an independent, publicly-traded company for the periods presented. Effective as of the spin-off spin-off Dover’s plan authorizes the granting stock options, stock-settled stock appreciation rights (“SARs”), restricted stock, and performance shares awards. The exercise price per share for SARs is equal to the closing price of Dover’s stock on the New York Stock Exchange on the date of grant. The period for which SARs and stock options are exercisable is fixed by Dover’s Compensation Committee at the time of grant. Generally, the stock options or SARs vest after three years of service and expire at the end of ten years. Performance share awards shall become vested if (1) Dover achieves certain specified internal metrics and (2) the employee remains continuously employed by Dover during the performance period. Partial vesting may occur after separation from service in the case of certain terminations not for cause and for retirements. Stock-based compensation costs are reported within Selling, general and administrative expenses. The following table summarizes the Company’s compensation expense relating to all stock-based incentive plans: Years Ended December 31, 2017 2016 2015 Pre-tax $ 2,236 $ 2,293 $ 1,925 Tax benefit (774 ) (787 ) (658 ) Total stock-based compensation expense, net of tax $ 1,462 $ 1,506 $ 1,267 SARs and Stock Options In 2017, 2016 and 2015, Dover issued SARs covering 82,240, 106,548 and 98,803 shares, respectively. Since 2006, Dover has only issued SARs. The fair value of each SAR granted was estimated on the date of grant using a Black-Scholes option-pricing model with the following assumptions: 2017 2016 2015 Risk-free interest rate 1.80 % 1.05 % 1.51 % Dividend yield 2.27 % 3.09 % 2.24 % Expected life (years) 4.6 4.6 5.1 Volatility 21.90 % 26.17 % 27.19 % Grant price $ 79.28 $ 57.25 $ 73.28 Fair value at date of grant $ 12.63 $ 9.25 $ 14.55 Expected volatilities are based on Dover’s stock price history, including implied volatilities from traded options on Dover’s stock. Dover uses historical data to estimate SAR exercise and employee termination patterns within the valuation model. The expected life of SARs granted is derived from the output of the option valuation model and represents the average period of time that SARs granted are expected to be outstanding. The interest rate for periods within the contractual life of the awards is based on the U.S. Treasury yield curve in effect at the time of grant. A summary of activity relating to SARs granted under the Dover plans for the year ended December 31, 2017 is as follows: SARs Number Weighted Weighted Outstanding at January 1, 2017 454,683 $ 63.69 Granted 82,240 79.28 Forfeited / expired (32,944 ) 67.10 Exercised (116,908 ) 61.93 Outstanding at December 31, 2017 387,071 67.17 6.7 Exercisable at December 31, 2017 157,078 $ 64.30 4.6 The following table summarizes information about outstanding SARs at December 31, 2017: SARs Outstanding SARs Exercisable Range of Exercise Number Weighted Exercise Weighted Remaining in Years Aggregate Number Weighted Exercise Weighted Remaining in Years Aggregate $ 25.96 - $37.79 23,816 $ 37.79 2.1 $ 1,505 23,816 $ 37.79 2.1 $ 1,505 $ 40.54 - $58.69 125,469 $ 57.52 6.7 5,454 38,309 $ 58.14 3.6 1,642 $ 63.33 - $82.51 237,786 $ 75.21 7.2 6,130 94,953 $ 73.44 5.7 2,616 387,071 $ 13,089 157,078 $ 5,763 Unrecognized compensation expense related to SARs not yet exercisable was $672 at December 31, 2017. This cost is expected to be recognized over a weighted average period of 1.7 years. Other information regarding the exercise of SARs and stock options is listed below: 2017 2016 2015 SARs Fair value of SARs that became exercisable $ 1,239 $ 1,564 $ 1,356 Aggregate intrinsic value of SARs exercised $ 2,787 $ 799 $ 1,874 Stock Options Cash received by Dover for exercise of stock options $ — $ — $ 100 Aggregate intrinsic value of options exercised $ — $ — $ 117 Performance Share Awards Performance share awards granted are expensed over the three-year requisite performance and service period. Awards become vested if (1) Dover achieves certain specified internal metrics and (2) the employee remains continuously employed by the Company during the performance period. Partial vesting may occur after separation from service in the case of certain terminations not for cause and for retirements. In 2017, 2016 and 2015, Dover issued performance shares to Apergy’s employees covering 4,162, 5,764 and 4,503 shares, respectively. The performance share awards granted in these years are considered performance condition awards as attainment is based on Dover’s performance relative to established internal metrics. The fair value of these awards was determined using Dover’s closing stock price on the date of grant. The expected attainment of the internal metrics for these awards is analyzed each reporting period, and the related expense is adjusted up or down based on expected attainment, if that attainment differs from previous estimates. The cumulative effect on current and prior periods of a change in attainment is recognized in compensation cost in the period of change. The fair value and average attainment used in determining compensation cost of the performance shares issued in 2017, 2016 and 2015 are as follows for the year ended December 31, 2017: Performance shares 2017 2016 2015 Fair value per share at date of grant $ 79.28 $ 57.25 $ 73.28 Average attainment rate reflected in expense 0.0 % 0.0 % 0.0 % A summary of activity for performance share awards for the year ended December 31, 2017 is as follows: Number Weighted Grant-Date Fair Value Unvested at January 1, 2017 10,267 $ 64.28 Granted 4,162 79.28 Vested (4,503 ) 73.28 Unvested at December 31, 2017 9,926 $ 66.49 There is no unrecognized compensation expense related to unvested performance shares as of December 31, 2017. The weighted average number of years over which compensation expense may be recognized for unvested performance shares is 1.0 year. Restricted Stock Units Dover also has restricted stock units authorized for grant. Common stock of Dover may be granted at no cost to certain officers and key employees. In general, restrictions limit the sale or transfer of these shares during a two-or-three-year period, and restrictions lapse proportionately over the two-or-three-year period. Dover granted 25,557, 42,117 and 17,263 of restricted stock units in 2017, 2016 and 2015, respectively. A summary of activity for restricted stock units for the year ended December 31, 2017 is as follows: Number Weighted Grant-Date Fair Value Unvested at January 1, 2017 54,064 $ 61.68 Granted 25,557 79.28 Forfeited (8,854 ) 64.07 Vested (20,712 ) 64.85 Unvested at December 31, 2017 50,055 $ 68.91 Unrecognized compensation expense relating to unvested restricted stock as of December 31, 2017 was $2,060, which will be recognized over a weighted average period of 1.6 years.

Employee Benefit Plans and Non-

Employee Benefit Plans and Non-Qualified Plans	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Employee Benefit Plans and Non-Qualified Plans	NOTE 16 — EMPLOYEE BENEFIT PLANS Prior to the Separation, certain of our employees participated in defined benefit and non-qualified Dover provided a defined benefit pension plan for its eligible U.S. employees and retirees (“U.S. Pension Plan”). As such, the portion of Apergy’s liability associated with the U.S. Pension Plan is not reflected in the condensed combined balance sheet as of December 31, 2017, and was not recorded at the Separation as this obligation will be maintained and serviced by Dover. Shortly before the Separation, Apergy participants in the U.S. Pension Plan (other than Norris USW participants) fully vested in their benefits, and all participants ceased accruing benefits. In addition, Apergy did not assume any funding requirements or obligations related to the U.S. Pension Plan upon the Separation. Norris USW participants were moved to a new pension plan and continued to accrue benefits. Dover also provided a defined benefit pension plan for its eligible salaried non-U.S. non-U.S. non-Apergy non-Apergy Dover provided to certain U.S. management employees, through non-qualified non-qualified non-qualified non-qualified At the Separation, we recognized $6.1 million of liabilities and $2.4 million of accumulated other comprehensive loss, net of tax, related to plans previously accounted for as multi-employer plans prior to the Separation. Net Periodic Benefit Cost Total net periodic benefit cost was $1.1 million and $1.2 million for the three months ended September 30, 2018 and 2017, respectively, and $2.9 million and $3.5 million for the nine months ended September 30, 2018 and 2017, respectively. Prior to the Separation, our net periodic benefit costs included total net periodic benefit costs associated with plans accounted for as single-employer plans and an allocation from Dover Corporation for plans accounted for as multi-employer plans. After the Separation, total net periodic benefit costs include all costs associated with plans that we sponsor, including plans that transferred to Apergy as discussed above. Defined Contribution Retirement Plans We also offer defined contribution retirement plans which cover the majority of our U.S. employees and employees in certain other countries. Expense relating to our defined contribution plans was $2.5 million and $2.1 million for the three months ended September 30, 2018 and 2017, respectively and $7.2 million and $6.1 million for the nine months ended September 30, 2018 and 2017, respectively.	14. Employee Benefit Plans and Non-Qualified Multiemployer Defined Benefit Plans and Non-Qualified Apergy participates in the following plans as though they are participants in a multi-employer plan with the other businesses of Dover. Accordingly, a proportionate share of the cost is reflected in the Combined Financial Statements. Dover provides a defined benefit pension plan for its eligible U.S. employees and retirees (the “U.S. Pension Plan”). As such, the portion of Apergy’s liability associated with this U.S. Pension Plan is not reflected in Apergy’s Combined Balance Sheets and will not be recorded at the distribution date as this obligation will be maintained and serviced by Dover. Shortly before the spin-off date, Apergy participants in this the U.S. Pension Plan (other than Norris USW participants) will fully vest in their benefits, and all participants will cease accruing benefits. In addition, Apergy will not assume any funding requirements or obligations related to the defined benefit pension plan upon the distribution date. Norris USW participants will be moved to a new pension plan, and will continue to accrue benefits at Dover pre-spin, and Apergy post-spin. Dover also provides an additional defined benefit pension plan for its eligible salaried non-U.S. employees and retirees in Canada. As such, the portion of Apergy’s liability associated with this non-U.S. plan is not reflected in Apergy’s Combined Balance Sheets as this obligation is being maintained and serviced by Dover. This plan, including all assets and liabilities, will be transferred to Apergy at the distribution date and will be recorded by Apergy at that point. Shortly before the spin-off date, all non-Apergy participants in this plan will cease accruing benefits or be permitted to make contributions, as applicable. The non-Apergy participants may elect a lump sum cash payment post separation that will be the responsibility of Apergy, will be funded out of the plan assets, and could also result in a non-cash settlement charge to earnings. Dover provides to certain U.S. management employees, through non-qualified plans, supplemental retirement benefits in excess of qualified plan limits imposed by federal tax law. The benefit obligation attributed to Apergy employees for these non-qualified plans will be reflected in Apergy’s Combined Balance Sheets as of the distribution date. As of the spin-off non-qualified The table below summarizes the expenses recorded in the Apergy financial statements for the Dover plans in which Apergy participates. Years Ended December 31, 2017 2016 2015 Plan Name Dover U.S. Pension Plan $ 3,922 $ 4,643 $ 4,783 Canada Salaried Pension Plan 554 1,615 513 Other non-qualified 108 121 123 No contributions were made by Dover to the U.S. Pension Plan in 2017, 2016 or 2015. No contribution is expected to be made in 2018. Contributions to the Canada Salaried Pension Plan totaled $1.8 million, $2.0 million, and $1.1 million in 2017, 2016 and 2015, respectively. Expected contributions in 2018 are $1.3 million. The non-qualified Single Employer Defined Benefit Plans Apergy sponsors one defined benefit pension plan to certain hourly non-U.S. employees and retirees. The plan is closed to new participants; however, all active participants in these plans continue to accrue benefits. This plan is considered a direct obligation of Apergy and has been recorded within Apergy’s Combined Financial Statements. The Company sponsors non-qualified Apergy does not have any other post-retirement employee benefit plans other than those plans mentioned above. Defined Contribution Plan Apergy offers a defined contribution retirement plan which covers the majority of its U.S. employees, as well as employees in certain other countries. The Company’s expense relating to defined contribution plans was $8,150, $6,446 and $7,247 for the years ended December 31, 2017, 2016 and 2015, respectively. Obligations and Funded Status The following tables summarize the Combined Balance Sheets impact, including the benefit obligations, assets and funded status associated with the Company’s single employer defined benefit plans at December 31, 2017 and 2016. Non-U.S. Qualified Defined Non-Qualified 2017 2016 2017 2016 Change in benefit obligation: Benefit obligation at beginning of year $ 3,512 $ 3,139 $ 18,600 $ 20,313 Service cost 106 102 — — Interest cost 137 129 621 719 Benefits paid (99 ) (79 ) (1,710 ) (2,484 ) Actuarial loss (gain) (22 ) 170 (3,314 ) 52 Currency translation and other 247 51 — — Benefit obligation at end of year 3,881 3,512 14,197 18,600 Change in plan assets: Fair value of plan assets at beginning of year 3,391 3,056 — — Actual return on plan assets 290 198 — — Company contributions 166 165 1,710 2,484 Benefits paid (99 ) (79 ) (1,710 ) (2,484 ) Currency translation and other 245 51 — — Fair value of plan assets at end of year 3,993 3,391 — — Funded (unfunded) status $ 112 $ (121 ) $ (14,197 ) $ (18,600 ) Amounts recognized in the Combined Balance Sheets consist of: Assets and Liabilities: Other assets and deferred charges $ 112 $ — $ — $ — Accrued compensation and employee benefits — — (1,547 ) (2,211 ) Other liabilities — (121 ) (12,650 ) (16,389 ) Total assets and liabilities 112 (121 ) (14,197 ) (18,600 ) Accumulated Other Comprehensive Loss (Income): Net actuarial losses 1,449 1,632 6,078 9,721 Prior service cost 40 42 — — Net asset at transition, other (20 ) (21 ) — — Deferred taxes (397 ) (446 ) (2,670 ) (3,592 ) Total accumulated other comprehensive loss, net of tax 1,072 1,207 3,408 6,129 Net amount recognized at December 31, $ 1,184 $ 1,086 $ (10,789 ) $ (12,471 ) Accumulated benefit obligations $ 3,881 $ 3,512 $ 14,197 $ 18,600 The Company’s net funded (unfunded) status at December 31, 2017 and 2016 was an asset of $112 and a liability of $121, respectively, relating to the Company’s defined pension benefit plan operated by the Company’s businesses in Canada. The accumulated benefit obligation for all defined benefit pension plans was $18,078 and $22,112 at December 31, 2017 and 2016, respectively. Pension plans with accumulated benefit obligations in excess of plan assets consist of the following at December 31, 2017 and 2016: 2017 2016 Projected benefit obligation (PBO) $ — $ 3,512 Accumulated benefit obligation (ABO) — 3,512 Fair value of plan assets — 3,391 Net Periodic Benefit Cost Components of the net periodic benefit cost were as follows: Defined Benefit Plans Non-U.S. Qualified Defined Benefit Plan Non-Qualified 2017 2016 2015 2017 2016 2015 Service cost $ 106 $ 102 $ 118 $ — $ — $ — Interest cost 137 129 130 621 719 708 Expected return on plan assets (198 ) (186 ) (184 ) — — — Amortization of: Prior service cost 2 2 2 — — — Recognized actuarial loss 68 58 57 330 305 284 Transition obligation (1 ) (1 ) (1 ) — — — Other — — — (1 ) — — Total net periodic benefit cost $ 114 $ 104 $ 122 $ 950 $ 1,024 $ 992 Amounts expected to be amortized from Accumulated other comprehensive income (loss) into net periodic benefit cost during 2018 are as follows: Non-U.S. Non-Qualified Amortization of: Prior service cost $ 2 $ — Recognized actuarial loss 55 205 Transition obligation (1 ) — Total $ 56 $ 205 Assumptions The Company determines actuarial assumptions on an annual basis. The weighted average assumptions used in determining the benefit obligations were as follows: Non-U.S. Non-Qualified 2017 2016 2017 2016 Discount rate 3.50 % 3.75 % 3.35 % 3.55 % The weighted average assumptions used in determining the net periodic benefit cost were as follows: Non-U.S. Non-Qualified 2017 2016 2017 2016 Discount rate 3.75 % 4.00 % 3.55 % 3.75 % Expected return on plan assets 5.50 % 5.75 % na na The Company’s discount rate assumption is determined by developing a yield curve based on high quality corporate bonds with maturities matching the plans’ expected benefit payment streams. The plans’ expected cash flows are then discounted by the resulting year-by-year Plan Assets The primary financial objective of the plans is to secure participant retirement benefits. Accordingly, the key objective in the plans’ financial management is to promote stability and, to the extent appropriate, growth in the funded status. Related and supporting financial objectives are established in conjunction with a review of current and projected plan financial requirements. As it relates to the funded defined benefit pension plans, including those accounted for as multi-employer plans, the Company’s funding policy is consistent with the funding requirements of the Employment Retirement Income Security Act (“ERISA”) and applicable international laws. The Company is responsible for overseeing the management of the investments of the plans’ assets and otherwise ensuring that the plans’ investment programs are in compliance with ERISA, other relevant legislation and related plan documents. Where relevant, the Company has retained professional investment managers to manage the plans’ assets and implement the investment process. The investment managers, in implementing their investment processes, have the authority and responsibility to select appropriate investments in the asset classes specified by the terms of their applicable prospectus or investment manager agreements with the plans. The assets of the plans are invested to achieve an appropriate return for the plans consistent with a prudent level of risk. The asset return objective is to achieve, as a minimum over time, the passively managed return earned by market index funds, weighted in the proportions outlined by the asset class exposures identified in the plans’ strategic allocation. The expected return on assets assumption used for pension expense is developed through analysis of historical market returns, statistical analysis, current market conditions and the past experience of plan asset investments. The Company’s plans were expected to achieve rates of return on invested assets of 5.50% and 5.75% for 2017 and 2016, respectively. The Company’s actual and target weighted average asset allocation for our non-U.S. 2017 2016 Current Equity securities 61 % 60 % 60 % Fixed income 38 % 39 % 40 % Real estate and other 1 % 1 % — % Total 100 % 100 % 100 % The fair values of the non-U.S. Non-U.S. December 31, 2017 December 31, 2016 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Mutual funds $ 2,399 $ 1,594 $ — $ 3,993 $ 2,104 $ 1,287 $ — $ 3,391 Total $ 2,399 $ 1,594 $ — $ 3,993 $ 2,104 $ 1,287 $ — $ 3,391 * A revision was made to the fair value leveling hierarchy in the above table as of December 31, 2016. The change was from level 2 to 1. The valuation techniques were unchanged and the amounts revised were not material to the prior annual period. The Company had no level 3 Non-U.S. Mutual funds are categorized as either Level 1 or 2 depending on the nature of the observable inputs. The methods described above may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, while the Company believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date. The availability of observable data is monitored by plan management to assess appropriate classification of financial instruments within the fair value hierarchy. Depending upon the availability of such inputs, specific securities may transfer between levels. In such instances, the transfer is reported at the end of the reporting period. Future Estimates Benefit Payments Estimated future benefit payments to retirees, which reflect expected future service, are as follows: Non-U.S. Non-Qualified 2018 $ 86 $ 1,572 2019 94 1,472 2020 92 1,368 2021 100 1,261 2022 107 1,154 2023 - 2027 709 4,163 Contributions In 2018, the Company expects to contribute approximately $0.2 million to its non-U.S.

Segment Information

Segment Information	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Information	NOTE 17 — SEGMENT INFORMATION We report our results of operations in the following reporting segments: Production & Automation Technologies and Drilling Technologies. Segment revenue and segment operating profit were as follows: Three Months Ended Nine Months Ended (in thousands) 2018 2017 2018 2017 Segment revenue: Production & Automation Technologies $ 241,214 $ 199,454 $ 696,591 $ 578,429 Drilling Technologies 75,254 59,200 209,727 166,664 Total revenue $ 316,468 $ 258,654 $ 906,318 $ 745,093 Income before income taxes: Segment operating profit: Production & Automation Technologies $ 24,257 $ 8,403 $ 57,957 $ 26,247 Drilling Technologies 26,209 20,420 71,738 55,067 Total segment operating profit 50,466 28,823 129,695 81,314 Corporate expense and other (1) 6,664 1,818 16,274 6,838 Interest expense, net 10,584 79 16,813 199 Income before income taxes $ 33,218 $ 26,926 $ 96,608 $ 74,277 (1) Corporate expense includes costs not directly attributable or allocated to our reporting segments such as corporate executive management and other administrative functions, costs related to our Separation from Dover Corporation and the results attributable to our noncontrolling interest.	16. Segment Information Historically the Company was part of the Dover Energy operating segment. As the Company is transitioning to a stand-alone company, the Company’s Chief Executive Officer, in his capacity as Chief Operating Decision Maker (“CODM”), evaluated how he views and measures the business performance. Based upon such evaluation, and effective during the fourth quarter of 2017, the Company determined it is organized into two operating segments, which are also its reportable segments, based on how the CODM analyzes performance, allocates capital and makes strategic and operational decisions. The CODM allocates resources to and evaluates the financial performance of each operating segment primarily based on revenues and segment earnings. The components of segment earnings were finalized in the fourth quarter 2017 in conjunction with the new segment structure to include the allocation of certain corporate expenses. The 2017, 2016 and 2015 segment results are presented on a comparable basis in accordance with the new segment structure. The segments were determined in accordance with FASB ASC Topic 280 — Segment Reporting and include i) Production & Automation Technologies and ii) Drilling Technologies. The segments are aligned around similar product applications serving Apergy’s key end markets, to enhance focus on end market strategies. • Production & Automation Technologies facilitates the efficient, safe and cost effective extraction of oil and gas. More specifically, Production & Automation Technologies designs, manufactures, markets and services a full range of artificial lift equipment, end-to-end Pro-Rod, • Drilling Technologies provides highly specialized products used in drilling oil and gas wells. Drilling Technologies designs, manufactures and markets polycrystalline diamond cutters (“PDCs”) for use in oil and gas drill bits under the US Synthetic brand. Over 95% of its PDCs are custom designed to meet unique customer requirements and are finished to exact customer specification to ensure optimal performance. PDCs are utilized in both vertical and horizontal drilling and need to be replaced as they wear out during the drilling process. Segment financial information and a reconciliation of segment results to combined results follows: Years Ended December 31, 2017 2016 2015 Revenue: Production & Automation Technologies $ 781,938 $ 638,017 $ 912,383 Drilling Technologies 227,653 113,320 164,297 Total combined revenue $ 1,009,591 $ 751,337 $ 1,076,680 Segment Income: Segment operating profit (loss) (1) Production & Automation Technologies (2) $ 24,889 $ (21,687 ) $ 58,446 Drilling Technologies 74,317 8,397 26,819 Total segment operating profit (loss) 99,206 (13,290 ) 85,265 Corporate expense / other (3) (10,852 ) (7,395 ) (9,436 ) Net income attributable to noncontrolling interest 930 1,851 1,436 Income (Loss) before income taxes $ 89,284 $ (18,834 ) $ 77,265 Depreciation and amortization: Production & Automation Technologies (4) $ 99,929 $ 99,607 $ 103,612 Drilling Technologies (5) 11,950 12,448 16,380 Combined total $ 111,879 $ 112,055 $ 119,992 Restructuring charges: Production & Automation Technologies $ 6,921 $ 12,757 $ 18,750 Drilling Technologies — 2,405 2,480 Combined total $ 6,921 $ 15,162 $ 21,230 Capital expenditures: Production & Automation Technologies $ 18,517 $ 21,588 $ 19,272 Drilling Technologies 8,171 4,137 4,945 Combined total $ 26,688 $ 25,725 $ 24,217 (1) Segment operating profit (loss) includes certain corporate expenses that are allocated to the segments such as information technology, supply chain, and shared services based on direct benefit where identifiable or other methods which the Company believes to be a reasonable reflection of the utilization of services provided. (2) Segment operating profit (loss) for Production & Automation Technologies excludes the net income attributable to noncontrolling interest. (3) Corporate expenses include those costs not attributable to a particular business segment such as corporate executive management and other corporate administrative functions. (4) Depreciation and amortization expense for Production & Automation Technologies includes acquisition-related depreciation and amortization of $57,426, $60,025 and $63,217 for the years ended December 31, 2017, 2016 and 2015, respectively. (5) Depreciation and amortization expense for Drilling Technologies includes acquisition-related depreciation and amortization of $24, $115 and $3,010 for the years ended December 31, 2017, 2016 and 2015, respectively. Total assets at December 31: 2017 2016 Production & Automation Technologies $ 1,683,782 $ 1,659,711 Drilling Technologies 220,993 191,184 Combined total $ 1,904,775 $ 1,850,895 Revenue classified by significant products and services were as follows: Years Ended December 31, 2017 2016 2015 Revenue: Artificial lift technologies $ 601,412 $ 499,033 $ 693,311 Automation technologies 82,093 65,351 93,639 Other production equipment 103,564 75,182 126,870 Drilling technologies 227,653 113,320 164,297 Intercompany eliminations (5) (5,131 ) (1,549 ) (1,437 ) Combined total $ 1,009,591 $ 751,337 $ 1,076,680 (5) Intercompany eliminations for the years ended December 31, 2017, 2016 and 2015 relate principally between the product groups automation technologies and artificial lift technologies. Information concerning principal geographic areas is presented as follows: Revenue Long-Lived Assets Years Ended December 31, At December 31, 2017 2016 2015 2017 2016 United States $ 769,928 $ 559,266 $ 808,549 $ 198,178 $ 184,268 Middle East 48,899 54,767 69,951 5,189 8,417 Canada 79,186 54,714 64,961 7,587 8,214 Europe 28,112 19,935 34,970 — — Australia 23,667 18,177 47,811 681 619 Latin & South America 34,368 23,588 23,208 197 229 Other 25,431 20,890 27,230 — — Combined total $ 1,009,591 $ 751,337 $ 1,076,680 $ 211,832 $ 201,747 Revenue is attributed to regions based on the location of the Company’s direct customer, which in some instances is an intermediary and not necessarily the end user. Long-lived assets are comprised of net property, plant and equipment. These assets have been classified based on the geographic location of where they reside. The Company’s businesses are based primarily in the United States of America, the Middle East and Canada. For the years ended December 31, 2017, 2016, and 2015 there were no customers that accounted for more than 10% of total revenues.

Condensed Consolidating Financi

Condensed Consolidating Financial Information	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Condensed Consolidating Financial Information	NOTE 18 — CONDENSED CONSOLIDATING FINANCIAL INFORMATION On May 3, 2018, and in connection with the Separation, Apergy completed the issuance of $300 million of senior notes, the payment obligations of which are fully and unconditionally guaranteed by certain 100-percent-owned • Apergy Corporation (issuer) • 100-percent-owned • All other non-guarantor • Adjustments necessary to present Apergy results on a consolidated basis. This condensed consolidating financial information should be read in conjunction with the accompanying consolidated financial statements and notes. Three Months Ended September 30, 2018 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Product revenue $ — $ 250,549 $ 32,553 $ — $ 283,102 Service revenue — 13,757 6,714 — 20,471 Lease and other revenue — 12,531 364 — 12,895 Related party revenue — 5,944 4,853 (10,797 ) — Total revenue — 282,781 44,484 (10,797 ) 316,468 Cost of goods and services — 175,718 37,899 (10,883 ) 202,734 Gross profit — 107,063 6,585 86 113,734 Selling, general and administrative expense 87 63,470 5,465 — 69,022 Interest expense, net 10,491 84 9 — 10,584 Other expense (income), net — (524 ) 1,434 — 910 Income (loss) before income taxes and equity in earnings of affiliates (10,578 ) 44,033 (323 ) 86 33,218 Provision for (benefit from) income taxes (2,575 ) 8,744 1,536 18 7,723 Income (loss) before equity in earnings of affiliates (8,003 ) 35,289 (1,859 ) 68 25,495 Equity in earnings of affiliates 33,266 5,344 12,604 (51,214 ) — Net income 25,263 40,633 10,745 (51,146 ) 25,495 Net income attributable to noncontrolling interest — — 232 — 232 Net income attributable to Apergy $ 25,263 $ 40,633 $ 10,513 $ (51,146 ) $ 25,263 Comprehensive income attributable to Apergy $ 25,187 $ 39,904 $ 11,166 $ (51,070 ) $ 25,187 Three Months Ended September 30, 2017 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Product revenue $ — $ 203,623 $ 32,225 $ — $ 235,848 Service revenue — 9,419 6,729 — 16,148 Lease and other revenue — 6,296 351 — 6,647 Related party revenue — 7,656 3,232 (10,877 ) 11 Total revenue — 226,994 42,537 (10,877 ) 258,654 Cost of goods and services — 148,389 36,261 (10,770 ) 173,880 Gross profit — 78,605 6,276 (107 ) 84,774 Selling, general and administrative expense — 50,448 4,380 — 54,828 Interest expense, net — 78 1 — 79 Other expense, net — 2,816 124 1 2,941 Income before income taxes and equity in earnings of affiliates — 25,263 1,771 (108 ) 26,926 Provision for income taxes — 7,938 340 (37 ) 8,241 Income before equity in earnings of affiliates — 17,325 1,431 (71 ) 18,685 Equity in earnings of affiliates 18,421 2,435 3,006 (23,862 ) — Net income 18,421 19,760 4,437 (23,933 ) 18,685 Net income attributable to noncontrolling interest — — 264 — 264 Net income attributable to Apergy $ 18,421 $ 19,760 $ 4,173 $ (23,933 ) $ 18,421 Comprehensive income attributable to Apergy $ 23,791 $ 20,195 $ 9,108 $ (29,303 ) $ 23,791 Nine Months Ended September 30, 2018 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Product revenue $ — $ 714,226 $ 94,084 $ — $ 808,310 Service revenue — 42,344 19,670 — 62,014 Lease and other revenue — 34,855 1,139 — 35,994 Related party revenue — 18,598 13,565 (32,163 ) — Total revenue — 810,023 128,458 (32,163 ) 906,318 Cost of goods and services — 515,005 111,142 (31,542 ) 594,605 Gross profit — 295,018 17,316 (621 ) 311,713 Selling, general and administrative expense 1,588 176,733 16,247 — 194,568 Interest expense, net 16,494 288 32 (1 ) 16,813 Other expense, net — 1,872 1,851 1 3,724 Income (loss) before income taxes and equity in earnings of affiliates (18,082 ) 116,125 (814 ) (621 ) 96,608 Provision for (benefit from) income taxes (4,217 ) 24,076 4,595 (130 ) 24,324 Income (loss) before equity in earnings of affiliates (13,865 ) 92,049 (5,409 ) (491 ) 72,284 Equity in earnings of affiliates 85,854 18,811 37,568 (142,233 ) — Net income 71,989 110,860 32,159 (142,724 ) 72,284 Net income attributable to noncontrolling interest — — 295 — 295 Net income attributable to Apergy $ 71,989 $ 110,860 $ 31,864 $ (142,724 ) $ 71,989 Comprehensive income attributable to Apergy $ 63,613 $ 110,214 $ 24,134 $ (134,348 ) $ 63,613 Nine Months Ended September 30, 2017 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Product revenue $ — $ 590,554 $ 89,283 $ — $ 679,837 Service revenue — 25,060 21,103 — 46,163 Lease and other revenue — 17,501 1,573 — 19,074 Related party revenue — 19,477 9,702 (29,160 ) 19 Total revenue — 652,592 121,661 (29,160 ) 745,093 Cost of goods and services — 425,792 103,259 (28,722 ) 500,329 Gross profit — 226,800 18,402 (438 ) 244,764 Selling, general and administrative expense — 149,145 13,214 — 162,359 Interest expense, net — 196 3 — 199 Other expense, net — 7,611 318 — 7,929 Income before income taxes and equity in earnings of affiliates — 69,848 4,867 (438 ) 74,277 Provision for income taxes — 22,726 400 (153 ) 22,973 Income before equity in earnings of affiliates — 47,122 4,467 (285 ) 51,304 Equity in earnings of affiliates 50,444 5,579 5,446 (61,469 ) — Net income 50,444 52,701 9,913 (61,754 ) 51,304 Net income attributable to noncontrolling interest — — 860 — 860 Net income attributable to Apergy $ 50,444 $ 52,701 $ 9,053 $ (61,754) $ 50,444 Comprehensive income attributable to Apergy $ 57,538 $ 53,055 $ 15,793 $ (68,848) $ 57,538 September 30, 2018 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Assets Cash and cash equivalents $ 108 $ 8,308 $ 9,598 $ — $ 18,014 Receivables — 245,950 40,797 (8,821 ) 277,926 Inventories — 189,536 31,146 (1,549 ) 219,133 Prepaid and other current assets 71 18,846 1,907 — 20,824 Total current assets 179 462,640 83,448 (10,370 ) 535,897 Property, plant and equipment, net — 222,425 13,642 — 236,067 Goodwill — 633,771 272,995 — 906,766 Advances due from affiliates 660,836 14,228 81,199 (756,263 ) — Intercompany notes receivable — 1,394 4 (1,398 ) — Investment in subsidiaries 978,944 688,890 542,462 (2,210,296 ) — Intangible assets, net — 207,694 89,703 — 297,397 Other assets and deferred charges 4,226 2,292 711 — 7,229 Total assets 1,644,185 2,233,334 1,084,164 (2,978,327 ) 1,983,356 Liabilities and Equity Accounts payable 30 113,497 22,397 (8,821 ) 127,103 Accrued compensation and employee benefits — 31,619 5,369 — 36,988 Other accrued expenses (3,811 ) 784,752 28,703 (756,590 ) 53,054 Total current liabilities (3,781 ) 929,868 56,469 (765,411 ) 217,145 Intercompany notes payable — 4 1,394 (1,398 ) — Long-term debt 683,206 4,321 16 — 687,543 Deferred income taxes — 73,089 20,049 — 93,138 Other long-term liabilities — 19,459 1,311 — 20,770 Total liabilities 679,425 1,026,741 79,239 (766,809 ) 1,018,596 Equity: Stockholders’ capital 964,760 1,213,290 1,034,542 (2,211,518 ) 1,001,074 Accumulated other comprehensive loss — (6,697 ) (31,830 ) — (38,527 ) Total stockholders’ equity 964,760 1,206,593 1,002,712 (2,211,518 ) 962,547 Noncontrolling interest — — 2,213 — 2,213 Total equity 964,760 1,206,593 1,004,925 (2,211,518 ) 964,760 Total liabilities and equity $ 1,644,185 $ 2,233,334 $ 1,084,164 $ (2,978,327 ) $ 1,983,356 December 31, 2017 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Assets Cash and cash equivalents $ — $ 5,763 $ 17,949 $ — $ 23,712 Receivables — 171,363 34,335 (3,674 ) 202,024 Inventories — 175,031 27,488 (928 ) 201,591 Prepaid and other current assets — 11,990 2,048 — 14,038 Total current assets — 364,147 81,820 (4,602 ) 441,365 Property, plant and equipment, net — 195,579 16,253 — 211,832 Goodwill — 633,734 276,354 — 910,088 Advances due from affiliates — 10,299 60,109 (70,408 ) — Investment in subsidiaries 1,640,034 801,235 388,315 (2,829,584 ) — Intangible assets, net — 234,795 103,715 — 338,510 Other assets and deferred charges — 2,129 851 — 2,980 Total assets 1,640,034 2,241,918 927,417 (2,904,594 ) 1,904,775 Liabilities and Equity Accounts payable — 83,864 18,636 (3,674 ) 98,826 Accrued compensation and employee benefits — 24,875 5,414 — 30,289 Other accrued expenses — 74,393 18,289 (70,732 ) 21,950 Total current liabilities — 183,132 42,339 (74,406 ) 151,065 Deferred income taxes — 75,075 21,910 — 96,985 Other liabilities — 16,657 34 — 16,691 Equity: Parent Company investment in Apergy 1,640,034 1,971,790 880,064 (2,830,188 ) 1,661,700 Accumulated other comprehensive loss — (4,736 ) (21,679 ) — (26,415 ) Total Parent Company equity 1,640,034 1,967,054 858,385 (2,830,188 ) 1,635,285 Noncontrolling interest — — 4,749 — 4,749 Total equity 1,640,034 1,967,054 863,134 (2,830,188 ) 1,640,034 Total liabilities and equity $ 1,640,034 $ 2,241,918 $ 927,417 $ (2,904,594 ) $ 1,904,775 Nine Months Ended September 30, 2018 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Cash provided (required) by operating activities $ (16,694 ) $ 103,911 $ 6,588 $ (999 ) $ 92,806 Cash provided (required) by investing activities: Capital expenditures — (43,746 ) (2,086 ) — (45,832 ) Proceeds from sale of property, plant, and equipment — 938 32 — 970 Purchase price adjustments on acquisition — — 53 — 53 Net cash required by investing activities — (42,808 ) (2,001 ) — (44,809 ) Cash provided (required) by financing activities: Proceeds from long-term debt, net of discounts 713,963 — — — 713,963 Payment of debt issue costs (16,006 ) — — — (16,006 ) Repayment of long-term debt (20,000 ) — — — (20,000 ) Advances due to/(from) affiliates (660,836 ) 677,999 (17,163 ) — — Net transfers to Parent Company and intercompany distributions (319 ) (736,557 ) 7,020 999 (728,857 ) Distributions to noncontrolling interest — — (2,720 ) — (2,720 ) Net cash provided (required) by financing activities 16,802 (58,558 ) (12,863 ) 999 (53,620 ) Effect of exchange rate changes on cash and cash equivalents — — (75 ) — (75 ) Net increase (decrease) in cash and cash equivalents 108 2,545 (8,351 ) — (5,698 ) Cash and cash equivalents at beginning of period — 5,763 17,949 — 23,712 Cash and cash equivalents at end of period $ 108 $ 8,308 $ 9,598 $ — $ 18,014 Nine Months Ended September 30, 2017 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Cash provided by operating activities $ — $ 38,153 $ 2,899 $ 153 $ 41,205 Cash provided (required) by investing activities: Capital expenditures — (28,221 ) (1,224 ) — (29,445 ) Proceeds from sale of property, plant, and equipment — 2,596 20 — 2,616 Net cash required by investing activities — (25,625 ) (1,204 ) — (26,829 ) Cash provided (required) by financing activities: Net transfers to Parent Company and intercompany distributions — (13,132 ) (5,935 ) (153 ) (19,220 ) Distributions to noncontrolling interest — — (1,212 ) — (1,212 ) Net cash required by financing activities — (13,132 ) (7,147 ) (153 ) (20,432 ) Effect of exchange rate changes on cash and cash equivalents — — 3,476 — 3,476 Net decrease in cash and cash equivalents — (604 ) (1,976 ) — (2,580 ) Cash and cash equivalents at beginning of period — 3,730 22,297 — 26,027 Cash and cash equivalents at end of period $ — $ 3,126 $ 20,321 $ — $ 23,447	20. Condensed Combining Financial Information On May 3, 2018, and in connection with the Separation, Apergy completed the issuance of $300 million of senior notes, the payment obligations of which are fully and unconditionally guaranteed by certain 100-percent-owned subsidiaries of Apergy on a joint and several basis. The following financial information presents the results of operations, financial position and cash flows for: • Apergy Corporation (issuer) • 100-percent-owned guarantor subsidiaries • All other non-guarantor subsidiaries • Adjustments necessary to present Apergy results on a combined basis. This condensed combining financial information should be read in conjunction with the accompanying combined financial statements and notes. Year Ended December 31, 2017 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments Total Revenue $ — $ 881,187 $ 164,507 $ (36,103 ) $ 1,009,591 Cost of goods and services — 586,519 140,516 (35,911 ) 691,124 Gross profit — 294,668 23,991 (192 ) 318,467 Selling, general and administrative expense — 200,839 18,678 — 219,517 Operating income (loss) — 93,829 5,313 (192 ) 98,950 Other expense, net — 9,429 237 — 9,666 Income before income taxes and equity in earnings of affiliates — 84,400 5,076 (192 ) 89,284 Benefit from income taxes — (10,680 ) (11,537 ) (67 ) (22,284 ) Income before equity in earnings of affiliates — 95,080 16,613 (125 ) 111,568 Equity in earnings of affiliates 110,638 22,110 11,020 (143,768 ) — Net income 110,638 117,190 27,633 (143,893 ) 111,568 Net income attributable to noncontrolling interest — — 930 — 930 Net income attributable to Apergy $ 110,638 $ 117,190 $ 26,703 $ (143,893 ) $ 110,638 Comprehensive income attributable to Apergy $ 117,852 $ 120,042 $ 31,065 $ (151,102 ) $ 117,852 Year Ended December 31, 2016 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments Total Revenue $ — $ 644,392 $ 142,614 $ (35,669 ) $ 751,337 Cost of goods and services — 459,465 132,350 (35,806 ) 556,009 Gross profit — 184,927 10,264 137 195,328 Selling, general and administrative expense — 183,892 21,517 — 205,409 Operating income (loss) — 1,035 (11,253 ) 137 (10,081 ) Other expense, net — 8,550 203 0 8,753 Loss before income taxes and equity in earnings of affiliates — (7,515 ) (11,456 ) 137 (18,834 ) Benefit from income taxes — (2,750 ) (5,341 ) 48 (8,043 ) Loss before equity in losses of affiliates — (4,765 ) (6,115 ) 89 (10,791 ) Equity in losses of affiliates (12,642 ) (23,668 ) (8,273 ) 44,583 — Net loss (12,642 ) (28,433 ) (14,388 ) 44,672 (10,791 ) Net income attributable to noncontrolling interest — — 1,851 — 1,851 Net loss attributable to Apergy $ (12,642 ) $ (28,433 ) $ (16,239 ) $ 44,672 $ (12,642 ) Comprehensive loss attributable to Apergy $ (11,577 ) $ (28,402 ) $ (15,205 ) $ 43,607 $ (11,577 ) Year Ended December 31, 2015 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments Total Revenue $ — $ 923,957 $ 192,682 $ (39,959 ) $ 1,076,680 Cost of goods and services — 604,715 177,504 (40,178 ) 742,041 Gross profit — 319,242 15,178 219 334,639 Selling, general and administrative expense — 220,897 24,826 — 245,723 Operating income (loss) — 98,345 (9,648 ) 219 88,916 Other expense (income), net — 10,606 (376 ) 1421 11,651 Income (loss) before income taxes and equity in earnings (losses) of affiliates — 87,739 (9,272 ) (1,202 ) 77,265 Provision for (benefit from) income taxes — 29,485 (5,431 ) 77 24,131 Income (loss) before equity in earnings of affiliates — 58,254 (3,841 ) (1,279 ) 53,134 Equity in earnings (losses) of affiliates 51,698 (17,980 ) 2,762 (36,480 ) — Net income (loss) 51,698 40,274 (1,079 ) (37,759 ) 53,134 Net income attributable to noncontrolling interest — — 1,436 — 1,436 Net income (loss) attributable to Apergy $ 51,698 $ 40,274 $ (2,515 ) $ (37,759 ) $ 51,698 Comprehensive income (loss) attributable to Apergy $ 39,738 $ 39,594 $ (13,795 ) $ (25,799 ) $ 39,738 December 31, 2017 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Assets Cash and cash equivalents $ — $ 5,763 $ 17,949 $ — $ 23,712 Receivables — 171,363 34,335 (3,674 ) 202,024 Inventories — 175,031 27,488 (928 ) 201,591 Prepaid and other current assets — 11,990 2,048 — 14,038 Total current assets — 364,147 81,820 (4,602 ) 441,365 Property, plant and equipment, net — 195,579 16,253 — 211,832 Goodwill — 633,734 276,354 — 910,088 Advances due from affiliates — 10,299 60,109 (70,408 ) — Investment in subsidiaries 1,640,034 801,235 388,315 (2,829,584 ) — Intangible assets, net — 234,795 103,715 — 338,510 Other assets and deferred charges — 2,129 851 — 2,980 Total assets 1,640,034 2,241,918 927,417 (2,904,594 ) 1,904,775 Liabilities and Equity Accounts payable — 83,864 18,636 (3,674 ) 98,826 Accrued compensation and employee benefits — 24,875 5,414 — 30,289 Other accrued expenses — 74,393 18,289 (70,732 ) 21,950 Total current liabilities — 183,132 42,339 (74,406 ) 151,065 Deferred income taxes — 75,075 21,910 — 96,985 Other liabilities — 16,657 34 — 16,691 Equity: Parent Company investment in Apergy 1,640,034 1,971,790 880,064 (2,830,188 ) 1,661,700 Accumulated other comprehensive loss — (4,736 ) (21,679 ) — (26,415 ) Total Parent Company equity 1,640,034 1,967,054 858,385 (2,830,188 ) 1,635,285 Noncontrolling interest — — 4,749 — 4,749 Total equity 1,640,034 1,967,054 863,134 (2,830,188 ) 1,640,034 Total liabilities and equity $ 1,640,034 $ 2,241,918 $ 927,417 $ (2,904,594 ) $ 1,904,775 December 31, 2016 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Assets Cash and cash equivalents $ — $ 3,730 $ 22,297 $ — $ 26,027 Receivables — 116,340 29,511 (6,366 ) 139,485 Inventories — 161,314 23,979 (735 ) 184,558 Prepaid and other current assets — 4,090 2,161 — 6,251 Total current assets — 285,474 77,948 (7,101 ) 356,321 Property, plant and equipment, net — 180,292 21,455 — 201,747 Goodwill — 633,734 268,845 — 902,579 Advances due from affiliates — 10,464 64,521 (74,985 ) — Investment in subsidiaries 1,551,353 753,916 348,046 (2,653,315 ) — Intangible assets, net — 273,127 113,690 — 386,817 Other assets and deferred charges — 2,499 932 — 3,431 Total assets 1,551,353 2,139,506 895,437 (2,735,401 ) 1,850,895 Liabilities and Equity Accounts payable — 53,195 19,451 (6,366 ) 66,280 Accrued compensation and employee benefits — 20,450 4,338 — 24,788 Other accrued expenses — 81,402 15,466 (75,242 ) 21,626 Total current liabilities — 155,047 39,255 (81,608 ) 112,694 Deferred income taxes — 125,490 42,075 — 167,565 Other liabilities — 19,009 274 — 19,283 Equity: Parent Company investment in Apergy 1,551,353 1,847,548 834,843 (2,653,793 ) 1,579,951 Accumulated other comprehensive loss — (7,588 ) (26,041 ) — (33,629 ) Total Parent Company equity 1,551,353 1,839,960 808,802 (2,653,793 ) 1,546,322 Noncontrolling interest — — 5,031 — 5,031 Total equity 1,551,353 1,839,960 813,833 (2,653,793 ) 1,551,353 Total liabilities and equity $ 1,551,353 $ 2,139,506 $ 895,437 $ (2,735,401 ) $ 1,850,895 Year Ended December 31, 2017 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Cash provided (required) by operating activities $ — $ 65,289 $ 11,561 $ 67 $ 76,917 Cash provided (required) by investing activities: Additions to property, plant and equipment — (39,565 ) (1,646 ) — (41,211 ) Proceeds from sale of property, plant, and equipment — 3,433 114 — 3,547 Acquisition (net of cash and cash equivalents acquired) — — (8,842 ) — (8,842 ) Net cash required by investing activities — (36,132 ) (10,374 ) — (46,506 ) Cash provided (required) by financing activities: Change in borrowings, net — — (599 ) — (599 ) Distributions to noncontrolling interest — — (1,212 ) — (1,212 ) Net transfers to Parent Company and intercompany distributions — (27,124 ) (4,001 ) (67 ) (31,192 ) Net cash required by financing activities — (27,124 ) (5,812 ) (67 ) (33,003 ) Effect of exchange rate changes on cash and cash equivalents — — 277 — 277 Net increase (decrease) in cash and cash equivalents — 2,033 (4,348 ) — (2,315 ) Cash and cash equivalents at beginning of period — 3,730 22,297 — 26,027 Cash and cash equivalents at end of period $ — $ 5,763 $ 17,949 $ — $ 23,712 Year Ended December 31, 2016 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Cash provided by operating activities $ — $ 103,788 $ 25,979 $ (48 ) $ 129,709 Cash provided (required) by investing activities: Additions to property, plant and equipment — (23,080 ) (3,774 ) — (26,854 ) Proceeds from sale of property, plant, and equipment — 2,245 281 — 2,526 Additions to intangible assets — (3,700 ) — — (3,700 ) Net cash required by investing activities — (24,535 ) (3,493 ) — (28,028 ) Cash provided (required) by financing activities: Distributions to noncontrolling interest — — (1,727 ) — (1,727 ) Net transfers to Parent Company and intercompany distributions — (78,232 ) (6,070 ) 48 (84,254 ) Net cash required by financing activities — (78,232 ) (7,797 ) 48 (85,981 ) Effect of exchange rate changes on cash and cash equivalents — — (90 ) — (90 ) Net increase in cash and cash equivalents — 1,011 14,599 — 15,610 Cash and cash equivalents at beginning of period — 2,719 7,698 — 10,417 Cash and cash equivalents at end of period $ — $ 3,730 $ 22,297 $ — $ 26,027 Year Ended December 31, 2015 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Cash provided (required) by operating activities $ — $ 137,352 $ 79,817 $ (1,498 ) $ 215,671 Cash provided (required) by investing activities: Additions to property, plant and equipment — (30,750 ) (1,235 ) — (31,985 ) Proceeds from sale of property, plant, and equipment — 3,814 4,070 — 7,884 Additions to intangible assets — (10,000 ) — — (10,000 ) Net cash provided (required) by investing activities — (36,936 ) 2,835 — (34,101 ) Cash provided (required) by financing activities: Net transfers to Parent Company and intercompany distributions — (108,909 ) (87,566 ) 1,498 (194,977 ) Net cash provided by (required by) financing activities — (108,909 ) (87,566 ) 1,498 (194,977 ) Effect of exchange rate changes on cash and cash equivalents — — (531 ) — (531 ) Net decrease in cash and cash equivalents — (8,493 ) (5,445 ) — (13,938 ) Cash and cash equivalents at beginning of period — 11,212 13,143 — 24,355 Cash and cash equivalents at end of period $ — $ 2,719 $ 7,698 $ — $ 10,417

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Description of Business Apergy is a leading provider of highly engineered technologies that help companies drill for and produce oil and gas efficiently and safely around the world. Its products include a full range of equipment and technologies that enable efficient drilling and safe and efficient production throughout the lifecycle of a well. Its principal products consist of artificial lift equipment and solutions, including electric submersible pump systems (“ESP”), rod pumping systems (“Rod Lift”), gas lift systems, progressive cavity pump systems (“PCP”) and plunger lift systems, as well as polycrystalline diamond cutters (“PDCs”) for drilling. The Company also provides a comprehensive automation offering consisting of equipment, software and Industrial Internet (“IIoT”) solutions for downhole monitoring, wellsite productivity enhancement and asset integrity management. The Company reports two business segments: Production & Automation Technologies and Drilling Technologies. For additional information on the Company’s segments, see Note 16 — Segment Information. In 2017, the Company acquired PCP Oil Tools S.A. and Ener Tools S.A., a supplier of progressive cavity pump products and services. This acquisition is part of the Production & Automation Technologies segment. Additionally, the Company did not make any acquisitions during the years ended December 31, 2016 and 2015. Combined Financial Statement Presentation The Combined Financial Statements have been derived from the consolidated financial statements and accounting records of Dover using the historical results of operations, and historical basis of assets and liabilities of Apergy and reflect Dover’s net investment in Apergy. Historically, stand-alone financial statements have not been prepared for Apergy. Management believes the assumptions underlying the allocations included in the Combined Financial Statements are reasonable. However, the Combined Financial Statements may not necessarily reflect Apergy’s results of operations, financial position and cash flows in the future, or what Apergy’s results of operations, financial position and cash flows would have been had Apergy been a stand-alone company during the periods presented herein. The Combined Financial Statements include the accounts of the Company. Intercompany accounts and transactions have been eliminated in consolidation. The results of operations of purchased businesses of Apergy are included from the date of acquisition. The accompanying financial statements include allocations of costs that were incurred by Dover for functions such as corporate executive management, human resources, information technology, facilities, tax, shared services, finance and legal, including the costs of salaries, benefits and other related costs. The total costs allocated to the accompanying Combined Financial Statements for these functions totaled approximately $22,987, $19,459 and $20,852 for the years ended December 31, 2017, 2016 and 2015, respectively, and are included in Selling, general and administrative expenses within the Combined Statements of Income. These expenses have been allocated to Apergy based on direct usage or benefit where identifiable, with the remainder allocated on the basis of revenues, headcount, or other measures. As a stand-alone public company, Apergy’s total costs related to such support functions may differ from the costs that were historically allocated to it from Dover. See Note 3 — Related Party Transactions for additional information regarding related party transactions. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the Combined Financial Statements and accompanying disclosures. These estimates may be adjusted due to changes in future economic, industry, or customer financial conditions, as well as changes in technology or demand. Estimates are used for, but not limited to, allowances for doubtful accounts receivable, net realizable value of inventories, restructuring reserves, warranty reserves, pension and post-retirement plans, stock-based compensation, useful lives for depreciation and amortization of long-lived assets, future cash flows associated with impairment testing for goodwill, indefinite-lived intangible assets and other long-lived assets, deferred tax assets, uncertain income tax positions and contingencies. Actual results may ultimately differ from estimates, although management does not believe such differences would materially affect the Combined Financial Statements in any individual year. Estimates and assumptions are periodically reviewed and the effects of revisions are reflected in the Combined Financial Statements in the period that they are determined. Cash and Cash Equivalents Cash and cash equivalents include cash on hand, demand deposits and short-term investments which are highly liquid in nature and have original maturities at the time of purchase of three months or less. The carrying value of cash and cash equivalents approximate fair value. Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable are recorded at face amounts less an allowance for doubtful accounts. The allowance is an estimate based on historical collection experience, current economic and market conditions and a review of the current status of each customer’s trade accounts receivable. Management evaluates the aging of the accounts receivable balances and the financial condition of its customers to estimate the amount of accounts receivable that may not be collected in the future and records the appropriate provision. Inventories Inventories for the majority of the Company’s subsidiaries, including all international subsidiaries, are stated at the lower of net realizable value, determined on the first-in, first-out Property, Plant and Equipment Property, plant and equipment includes the historical cost of land, buildings, machinery and equipment, purchased software and significant improvements to existing plant and equipment or, in the case of acquisitions, a fair market value appraisal of assets. Expenditures for maintenance, repairs and minor renewals are expensed as incurred. When property or equipment is sold or otherwise disposed of, the related cost and accumulated depreciation is removed from the respective accounts and the gain or loss realized on disposition is reflected in earnings. The Company depreciates its assets on a straight-line basis over their estimated useful lives as follows: buildings and improvements 5 to 31.5 years; machinery and equipment 3 to 7 years; furniture and fixtures 3 to 7 years; vehicles 3 years; and software 3 to 10 years. Derivative Financial Instruments The Company uses derivative financial instruments to hedge its exposure to foreign currency exchange rate risk. The Company does not enter into derivative financial instruments for speculative purposes and has a portfolio of derivatives that is not material in value. Derivative financial instruments used for hedging purposes must be designated and effective as a hedge of the identified risk exposure at inception of the contract. For derivatives hedging the fair value of assets or liabilities, the changes in fair value of both the derivatives and of the hedged items are recorded in current earnings. Goodwill, Other Intangible Assets and Long-Lived Assets Goodwill represents the excess of purchase price over the fair value of net assets acquired. Goodwill and certain other intangible assets deemed to have indefinite lives (trademarks) are not amortized. For goodwill, impairment tests are required at least annually, or more frequently if events or circumstances indicate that it may be impaired, or when some portion but not all of a reporting unit is disposed. Historically, the Company was part of the Dover Energy operating segment. Based on its historical organizational structure, the Company identified two reporting units for which cash flows are determinable and to which goodwill may be allocated. Effective in the fourth quarter of 2017, the Company determined it is organized into a new segment structure discussed in Note 16 — Segment Information comprised of two reporting units, to which goodwill may be allocated. The Company performs its goodwill impairment test annually in the fourth quarter at the reporting unit level. A quantitative test is used to determine existence of goodwill impairment and the amount of the impairment loss at the reporting unit level. The quantitative test compares the fair value of a reporting unit with its carrying amount, including goodwill. The Company uses an income-based valuation method, determining the present value of estimated future cash flows, to estimate the fair value of a reporting unit. If the fair value of a reporting unit exceeds its carrying amount, goodwill of the reporting unit is not impaired. If the carrying amount of a reporting unit exceeds its fair value, an impairment loss shall be recognized in an amount equal to that excess, limited to the total amount of goodwill allocated to that reporting unit. Factors used in the impairment analysis require significant judgment, and actual results may differ from assumed and estimated amounts. The Company uses its own market assumptions including internal projections of future cash flows, discount rates and other assumptions considered reasonable and inherent in the analysis. These forecasts are based on historical performance and future estimated results. The discount rates used in these analyses vary by reporting unit and are based on a capital asset pricing model and published relevant industry rates. The Company uses discount rates commensurate with the risks and uncertainties inherent to each reporting unit and in the internally developed forecasts. See Note 7 — Goodwill and Other Intangible Assets for further discussion of the Company’s annual goodwill impairment test and results. The Company uses an income-based valuation method to test its indefinite-lived intangible assets for impairment, at least annually. The fair value of the intangible asset is compared to its carrying value. This method uses the Company’s own market assumptions considered reasonable and inherent in the analysis. Any excess of carrying value over the estimated fair value is recognized as an impairment loss. No impairment of indefinite-lived intangible assets was required for the years ended December 31, 2017, 2016 and 2015. Other intangible assets with determinable lives consist primarily of customer intangibles, unpatented technologies, patents and trademarks. These other intangibles are amortized over their estimated useful lives, ranging from 5 to 15 years. Long-lived assets (including definite-lived intangible assets) are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable, such as a significant sustained change in the business climate. If an indicator of impairment exists for any grouping of assets, an estimate of undiscounted future cash flows is produced and compared to its carrying value. If an asset is determined to be impaired, the loss is measured by the excess of the carrying amount of the asset over its fair value as determined by an estimate of discounted future cash flows. Restructuring Accruals From time to time, the Company takes actions to reduce headcount, close facilities, or otherwise exit operations. Such restructuring activities at an operation are recorded when management has committed to an exit or reorganization plan and when termination benefits are probable and can be reasonably estimated based on circumstances at the time the restructuring plan is approved by management or when termination benefits are communicated. Exit costs include future minimum lease payments on vacated facilities and other contractual terminations. In addition, asset impairments may be recorded as a result of an approved restructuring plan. The accrual of both severance and exit costs requires the use of estimates. Though the Company believes that its estimates accurately reflect the anticipated costs, actual results may differ from the original estimated amounts. Noncontrolling interests A noncontrolling interest represents the equity interest in a subsidiary that is not attributable, either directly or indirectly, to the Company and is reported as equity, separately from the Company’s controlling interests. The noncontrolling interest relates to the Company’s ownership interest in Norris Production Solutions Middle East LLC, a subsidiary company in the Sultanate of Oman with a local partner, where the Company is the majority owner at 60% and has the controlling financial interest. The outside investor’s interests in this subsidiary company are included in noncontrolling interest in the Company’s Combined Financial Statements. Foreign Currency Assets and liabilities of non-U.S. subsidiaries, where the functional currency is not the U.S. dollar, have been translated at year-end exchange rates and profit and loss accounts have been translated using weighted-average monthly exchange rates. Foreign currency translation gains and losses are included in the Combined Statements of Comprehensive Income as a component of Other comprehensive income (loss). Assets and liabilities of an entity that are denominated in currencies other than an entity’s functional currency are re-measured into the functional currency using end of period exchange rates or historical rates where applicable to certain balances. Gains and losses related to these re-measurements are recorded within the Combined Statements of Income as a component of Other expense, net. Revenue Recognition Revenue is recognized when all of the following conditions are satisfied: a) persuasive evidence of an arrangement exists, b) price is fixed or determinable, c) collectability is reasonably assured and d) delivery has occurred or services have been rendered. The majority of the Company’s revenue is generated through the manufacture and sale of a broad range of specialized products and components, with revenue recognized upon transfer of title and risk of loss, which is generally upon shipment. Certain product sales are recognized based on the percentage-of-completion In limited cases, revenue arrangements with customers require delivery, installation, testing, or other acceptance provisions to be satisfied before revenue is recognized. The Company includes shipping costs billed to customers in revenue and the related shipping costs in cost of goods and services. Stock-Based Compensation The Company’s employees have historically participated in Dover’s stock-based compensation plans. Stock-based compensation has been allocated to the Company based on the awards and terms previously granted to the Company’s employees. The principal awards issued under the stock-based compensation plans include stock options, stock-settled stock appreciation rights, restricted stock units and performance share awards. The cost of such awards is measured at the grant date based on the fair value of the award. At the time of grant, Dover estimates forfeitures, based on historical experience, in order to estimate the portion of the award that will ultimately vest. The value of the portion of the award that is expected to ultimately vest is recognized as expense on a straight-line basis, generally over the explicit service period of three years (except for retirement-eligible employees and retirees) and is included in Selling, general and administrative expenses in the Combined Statements of Income. Expense for awards granted to retirement-eligible employees is recorded over the period from the date of grant through the date the employee first becomes eligible to retire and is no longer required to provide service. See Note 12 — Equity and Cash Incentive Program for additional information related to stock-based compensation. Employee Benefit Plans Apergy participates in defined benefit plans and non-qualified supplemental retirement plans sponsored by Dover that are accounted for as multi-employer plans in the Combined Financial Statements. Apergy also sponsors a defined benefit plan and non-qualified plan. These plans are accounted for as single employer plans in the Combined Financial Statements. Apergy also offers a defined contribution plan. See Note 14 — Employee Benefit Plans and Non-Qualified Plans for additional information. Income Taxes The Company’s operations have historically been included in Dover’s consolidated federal tax return and certain combined state returns. The income tax expense in these Combined Financial Statements has been determined on a stand-alone return basis in accordance with Accounting Standards Codification (“ASC”) 740 “Income Taxes,” which requires the recognition of income taxes using the liability method. Under this method, the Company is assumed to have historically filed a return separate from Dover, reporting its taxable income or loss and paying applicable tax based on its separate taxable income and associated tax attributes in each tax jurisdiction. Income taxes payable at each balance sheet date computed under the stand-alone return basis are classified within Parent Company investment in Apergy since Dover is legally liable for the tax. Accordingly, changes in income taxes payable are recorded as a component of financing activities in the Combined Statements of Cash Flows. The calculation of income taxes on the separate return basis requires considerable judgment and the use of both estimates and allocations. As a result, the Company’s effective tax rate and deferred tax balances will differ significantly from those in Dover’s historic periods. Additionally, the Company’s deferred tax balances as calculated on the separate return basis will differ from the deferred tax balances of Dover, if legally separated. See Note 11 — Income Taxes for additional information on the Company’s income taxes and unrecognized tax benefits. The U.S. bill commonly referred to as the Tax Cuts and Jobs Act (“Tax Reform Act”), which was enacted on December 22, 2017, significantly changes U.S. tax law by, among other things, lowering corporate income tax rates, implementing a territorial tax system and imposing a repatriation tax on deemed repatriated earnings of foreign subsidiaries. The Tax Reform Act permanently reduces the U.S. corporate income tax rate from a maximum of 35% to a flat 21% rate, effective January 1, 2018. The Tax Reform Act also provided for a one-time deemed repatriation of post-1986 undistributed foreign subsidiary earnings and profits through the year ended December 31, 2017. The Global Intangible Low-Taxed Income (“GILTI”) provisions require the Company to include in its U.S. income tax return foreign subsidiary earnings in excess of an allowable return on the foreign subsidiary’s tangible assets. The Company expects that it will be subject to incremental U.S. tax on GILTI income beginning in 2018, due to expense allocations required by the U.S. foreign tax credit rules. The Company has elected to account for GILTI tax in the period in which it is incurred, and therefore has not provided any deferred tax impacts of GILTI in its combined financial statements for the year ended December 31, 2017. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118 (“SAB 118”) to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Reform Act. The Company has recognized the provisional tax impacts related to deemed repatriated earnings and the benefit for the revaluation of deferred tax assets and liabilities, and included these amounts in its combined financial statements for the year ended December 31, 2017. The final impact may differ from these provisional amounts, possibly materially, due to, among other things, additional analysis, changes in interpretations and assumptions the Company has made, additional regulatory guidance that may be issued, and actions the Company may take as a result of the Tax Reform Act. In accordance with SAB 118, the financial reporting impact of the Tax Reform Act will be completed in the fourth quarter of 2018. Research and Development Costs Research and development costs, including qualifying engineering costs, are expensed when incurred and amounted to $18,501, $16,511 and $19,255, in 2017, 2016 and 2015, respectively. Advertising Costs Advertising costs are expensed when incurred and amounted to $1,220, $825 and $1,604, in 2017, 2016 and 2015, respectively. Risk, Retention, Insurance Apergy was covered under Dover’s insurance policies during the years ended December 31, 2017 and 2016. For both years ended December 31, 2017 and 2016, Dover self-insured its product and commercial general liability claims up to $5.0 million per occurrence and automobile liability claims up to $1.0 million per occurrence. For the years ended December 31, 2017 and 2016, Dover self-insured its workers’ compensation claims up to $0.8 million per occurrence, respectively. Third-party insurance provides primary level coverage in excess of these amounts up to certain specified limits. In addition, Dover has excess liability insurance from third-party insurers on both an aggregate and an individual occurrence basis well in excess of the limits of the primary coverage. A worldwide program of property insurance covers Dover’s owned and leased property and any business interruptions that may occur due to an insured hazard affecting those properties, subject to reasonable deductibles and aggregate limits. Dover’s property and casualty insurance programs contain various deductibles that, based on Dover’s experience, are typical and customary for a company of its size and risk profile. Apergy does not consider any of the deductibles under the Dover program to represent a material risk to Apergy. Dover generally maintains deductibles for claims and liabilities related primarily to workers’ compensation, health and welfare claims, general commercial, product and automobile liability and property damage and business interruption resulting from certain events. Dover accrues for claim exposures that are probable of occurrence and can be reasonably estimated. As part of Dover’s risk management program, insurance is maintained to transfer risk beyond the level of self-retention and provide protection on both an individual claim and annual aggregate basis. Reclassifications We changed our presentation of expenditures related to purchases of leased inventory. Previously, these amounts were reported in the operating section of our cash flow statement as “other” in adjustments to reconcile net income but are now reported as changes in our operating assets and liabilities in the operating section of our cash flow statement as “leased assets and other, net.” We changed our presentation of amortization expense primarily related to customer intangible assets. For the years ended December 31, 2017, 2016 and 2015, we reclassified $42.9 million, $45.2 million and $48.3 million of amortization expense previously reported as a component of “selling, general and administrative expense” to “cost of goods and services” on our combined statements of income. Certain amounts in prior years have been reclassified to conform to the current year presentation. Recent Accounting Pronouncements Recently Issued Accounting Standards The following standards, issued by the Financial Accounting Standards Board (“FASB”), will, or are expected to, result in a change in practice and/or have a financial impact to the Company’s Combined Financial Statements: In March 2017, the FASB issued Accounting Standards Update (“ASU”) 2017-07, In January 2017, the FASB issued ASU 2017-01, In February 2016, the FASB issued ASU 2016-02, After the Separation from Dover, we developed a project plan and established a cross-functional team to continue the process of implementing the new guidance, which included an evaluation of the work performed by Dover prior to the Separation. We made progress on our plan including gathering information on all leases, surveying our business, assessing our portfolio of leases and compiling a central repository of active leases. During the third quarter of 2018, we completed diagnostic reviews of certain sampled leases to support our policy elections. Additionally, we made significant progress configuring and implementing a new lease software system. We continue to evaluate our policy elections and considerations under the new lease guidance, including the potential use of practical expedients, and we are in the process of updating our internal control and business processes. As we continue to assess the impact the guidance will have on our financial statements and related disclosures, internal control over financial reporting and other business practices and processes, we expect to recognize right of use assets and liabilities for operating leases in our consolidated balance sheet upon adoption. In May 2014, the FASB issued ASU 2014-09, which the entity expects to be entitled, in exchange for those goods or services. This ASU also requires disclosures sufficient to enable users to understand the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers, including qualitative and quantitative disclosures about contracts with customers, significant judgments and changes in judgments and assets recognized from the costs to obtain or fulfill a contract. This guidance is effective for the Company on January 1, 2018. Dover commenced its assessment of ASU 2014-09 Recently Adopted Accounting Standards Effective January 1, 2018, we adopted ASU 2016-15, In January 2017, the FASB issued ASU 2017-04, In July 2015, the FASB issued ASU 2015-11,

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisitions	4. Acquisitions 2017 On October 2, 2017, the Company acquired 100% of the voting stock of PCP Oil Tools S.A. and Ener Tools S.A. (“PCP”), a supplier of progressive cavity pump products and services for total consideration of $8,842, net of cash acquired. This acquisition is a part of the Production & Automation Technologies segment and will broaden the Company’s ability to supply Argentina with additional products to customers. The goodwill recorded as a result of this acquisition reflects the benefits expected to be derived from product line expansion and operational synergies. The Company recorded non-deductible goodwill of $5,053 and customer intangible assets of $4,538. The intangible assets are being amortized over 9 years. The pro forma effects of this acquisition on the Company’s operations were not material.

Other Accrued Expenses and Othe

Other Accrued Expenses and Other Liabilities	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Other Accrued Expenses and Other Liabilities	8. Other Accrued Expenses and Other Liabilities The following table details the major components of Other accrued expenses (current): December 31, December 31, Unearned/deferred revenue $ 4,487 $ 3,787 Warranty 2,978 4,568 Restructuring and exit costs 2,551 459 Taxes other than income 2,432 1,424 Accrued freight, travel and transportation 1,397 1,384 Short-term capital lease obligations 1,041 694 Accrued rebates 617 473 Other (none of which are individually significant) 6,447 8,837 Total other accrued expenses $ 21,950 $ 21,626 The following table details the major components of Other liabilities (noncurrent): December 31, December 31, Defined benefit and other post-retirement benefit plans $ 12,650 $ 16,510 Long-term capital lease obligations 3,742 1,919 Warranty 92 98 Other (none of which are individually significant) 207 756 Total other liabilities $ 16,691 $ 19,283 Warranty Estimated warranty program claims are provided for at the time of sale. Amounts provided for are based on historical costs, claims experience and adjusted for new claims. The changes in the carrying amount of product warranties were as follows: Years Ended December 31, 2017 2016 2015 Balance, beginning of year $ 4,666 $ 4,421 $ 6,717 Provision for warranties 309 2,109 1,266 Settlements made (1,896 ) (1,518 ) (3,168 ) Other adjustments, including currency translation (9 ) (346 ) (394 ) Balance, end of year $ 3,070 $ 4,666 $ 4,421

Pro Forma Information (unaudite

Pro Forma Information (unaudited)	12 Months Ended
	Dec. 31, 2017
Text Block [Abstract]
Pro Forma Information (unaudited)	17. Pro Forma Information (unaudited) Pro forma shareholders’ equity (unaudited) is based upon the Company’s historical Parent Company equity as of December 31, 2017, and has been computed to give effect to the following pro forma adjustments: • the expected transfer to Apergy, upon the spin-off, • the distribution of $700.0 million from Apergy to Dover immediately prior to the distribution using proceeds from the incurrence of $702.5 million of new indebtedness in connection with the separation; • expected tax liabilities for reimbursement to Dover under the tax matters agreement • the reclassification of Dover’s remaining net investment in Apergy to additional paid-in • the distribution of approximately 77.4 million shares of Apergy’s common stock at a par value of $0.01 per share

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	18. Subsequent Events (unaudited) Separation from Dover Corporation On April 18, 2018, the Dover Corporation Board of Directors approved the separation of entities conducting its upstream oil and gas energy business within Dover’s Energy segment (the “Separation”) into an independent, publicly traded company named Apergy Corporation. Apergy Corporation was incorporated in Delaware on October 10, 2017, under the name Wellsite Corporation and was renamed Apergy Corporation on February 2, 2018. Apergy Corporation was formed for the purpose of holding entities, assets and liabilities conducting Dover’s upstream oil and gas business within Dover’s Energy segment. In accordance with the separation and distribution agreement, the two companies were separated by Dover distributing to Dover’s stockholders all 77,339,828 shares of common stock of Apergy on May 9, 2018. Each Dover shareholder received one share of Apergy stock for every two shares of Dover stock held at the close of business on the record date of April 30, 2018. In conjunction with the Separation, Dover received a private letter ruling from the Internal Revenue Service to the effect that, based on certain facts, assumptions, representations and undertakings set forth in the ruling, for U.S. federal income tax purposes, the distribution of Apergy common stock was not taxable to Dover or U.S. holders of Dover common stock, except in respect to cash received in lieu of fractional share interests. Following the Separation, Dover retained no ownership interest in Apergy, and each company, as of May 9, 2018, has separate public ownership, boards of directors and management. In connection with the Separation and as described below, we incurred an aggregate principal amount of $715 million of long-term debt, which consisted of a $415 million term loan facility and $300 million of senior notes. Net proceeds from the notes offering, together with borrowings under the term loan facility, were used to make a cash payment of $700 million to Dover and to pay fees and expenses incurred in connection with the Separation. Issuances of Debt Senior Notes On May 3, 2018, and in connection with the Separation, we completed the private placement of $300 million in aggregate principal amount of 6.375% senior notes due May 2026 (“Senior Notes”). Interest on the Senior Notes is payable semi-annually in arrears on May 1 and November 1 of each year, commencing on November 1, 2018. Net proceeds of $293.8 million from the offering were utilized to partially fund the $700 million cash payment to Dover at the Separation and to pay fees and expenses incurred in connection with the Separation. In connection with the private placement, we granted the initial purchasers of the Senior Notes certain registration rights under a registration right agreement. We have agreed for the benefit of the holders of the Senior Notes to use our commercially reasonable efforts to file and cause to be effective a registration statement with the SEC relating to a registered offer to exchange the Senior Notes for an issue of SEC-registered notes with terms identical in all material respects to the Senior Notes. Generally, we have one year from the issuance of the Senior Notes to complete the exchange offer. Should Apergy not complete its obligations under the registration rights agreement within a year, the annual interest rate on the Senior Notes will increase at different intervals based on the passage of time after one year. Senior Secured Credit Facilities On May 9, 2018, Apergy entered into a credit agreement (“credit agreement”) governing the terms of its new senior secured credit facilities, consisting of (i) a seven-year senior secured term loan B facility (“term loan facility”) and (ii) a five-year senior secured revolving credit facility (“revolving credit facility,” and together with the term loan facility, the “senior secured credit facilities”), with JPMorgan Chase Bank, N.A. as administrative agent. The net proceeds of the senior secured credit facilities were used (i) to pay fees and expenses in connection with the Separation, (ii) partially fund the cash payment to Dover and (iii) provide for working capital and other general corporate purposes. The senior secured credit facilities are jointly and severally guaranteed by Apergy and certain of Apergy’s wholly owned U.S. subsidiaries (“guarantors”), on a senior secured basis, and are secured by substantially all tangible and intangible assets of Apergy and the guarantors, except for certain excluded assets.

Quarterly Information (Unaudite

Quarterly Information (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Information (Unaudited)	19. Quarterly Information (Unaudited) 2017 2016 (in thousands, except per share data) 4th Qtr. 3rd Qtr. 2nd Qtr. 1st Qtr. 4th Qtr. 3rd Qtr. 2nd Qtr. 1st Qtr. Revenue $ 264,498 $ 258,654 $ 256,161 $ 230,278 $ 201,176 $ 185,455 $ 168,535 $ 196,171 Gross profit 73,703 84,774 84,630 75,360 61,012 47,254 32,610 54,452 Net income (loss) 60,264 18,685 19,033 13,586 4,167 (2,154 ) (10,294 ) (2,510 ) Net income (loss) attributable to Apergy 60,194 18,421 18,754 13,269 3,769 (2,503 ) (10,872 ) (3,036 ) Basic earnings per share (1) $ 0.78 $ 0.24 $ 0.24 $ 0.17 $ 0.05 $ (0.03 ) $ (0.14 ) $ (0.04 ) Diluted earnings per share (1) $ 0.77 $ 0.24 $ 0.24 $ 0.17 $ 0.05 $ (0.03 ) $ (0.14 ) $ (0.04 ) (1) On May 9, 2018, 77,339,828 shares of our common stock were distributed to Dover stockholders in conjunction with the Separation. For comparative purposes, we have assumed the shares issued in conjunction with the Separation to be outstanding as of the beginning of each period prior to the Separation. In addition, we have assumed the potential dilutive securities outstanding as of May 8, 2018, were outstanding and fully dilutive in each of the periods prior to the Separation.

Schedule II Valuation and Quali

Schedule II Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II Valuation and Qualifying Accounts	SCHEDULE II Years Ended December 31, 2017, 2016 and 2015 (In thousands) Allowance for Doubtful Accounts Balance at Beginning of Year Charged to Expense (A) Accounts Written Other Balance at End of Year Ended December 31, 2017 $ 5,634 954 (1,882 ) 47 $ 4,753 Year Ended December 31, 2016 $ 4,431 2,941 (1,469 ) (269 ) $ 5,634 Year Ended December 31, 2015 $ 3,510 2,154 (1,159 ) (74 ) $ 4,431 (A)  Net of recoveries on previously reserved or written-off    Deferred Tax Valuation Allowance Balance at Beginning of Year Additions Reductions Other Balance at End of Year Ended December 31, 2017 $ 1,082 198 — — $ 1,280 Year Ended December 31, 2016 $ 64 1,018 — — $ 1,082 Year Ended December 31, 2015 $ 50 14 — — $ 64 LIFO Reserve Balance at Beginning of Year Charged to Reductions Other Balance at End of Year Ended December 31, 2017 $ 9,381 1,175 — — $ 10,556 Year Ended December 31, 2016 $ 12,933 — (3,552 ) — $ 9,381 Year Ended December 31, 2015 $ 15,214 — (2,281 ) — $ 12,933

Basis of Presentation and Sep_2

Basis of Presentation and Separation (Policies)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation Prior to the Separation, our results of operations, financial position and cash flows were derived from the consolidated financial statements and accounting records of Dover and reflect the combined historical results of operations, financial position and cash flows of certain Dover entities conducting its upstream oil and gas energy business within Dover’s Energy segment, including an allocated portion of Dover’s corporate costs. These financial statements have been presented as if such businesses had been combined for all periods prior to the Separation. All intercompany transactions and accounts within Dover were eliminated. The assets and liabilities were reflected on a historical cost basis since all of the assets and liabilities presented were wholly owned by Dover and were transferred within the Dover consolidated group. The statements of income also include expense allocations for certain corporate functions historically performed by Dover and not allocated to its operating segments, including corporate executive management, human resources, information technology, facilities, tax, shared services, finance and legal, including the costs of salaries, benefits and other related costs. These expense allocations were based on direct usage or benefit where identifiable, with the remainder allocated on the basis of revenue, headcount or other measures. These pre-Separation Prior to the Separation, transactions between Apergy and Dover, with the exception of transactions discussed in Note 3 — Related Party Transactions, are reflected in the condensed combined balance sheet as of December 31, 2017, as part of “Net parent investment in Apergy” and in the condensed combined statements of cash flows as a financing activity in “Distributions to Dover Corporation, net.” See Note 3 — Related Party Transactions for additional information. No portion of Dover’s third-party debt was historically held by an Apergy entity or was transferred to Apergy; therefore, no debt was included in the condensed combined balance sheet as of December 31, 2017, and no interest expense was presented in the condensed combined statement of income for the three and nine months ended September 30, 2017. Intercompany notes payable to Dover of $224.5 million as of December 31, 2017, were presented within “Net parent investment in Apergy” because the notes were not settled in cash. Accordingly, no interest expense related to intercompany debt was presented in the condensed combined statements of income for each of the periods presented prior to the Separation. Additionally, our U.S. cash was historically pooled to Dover through intercompany advances and consequently is not reflected on our condensed combined balance sheet as of December 31, 2017. All financial information presented after the Separation represents the consolidated results of operations, financial position and cash flows of Apergy. Accordingly, our results of operations and cash flows consist of the consolidated results of Apergy from May 9, 2018 to September 30, 2018, and the combined results of operations and cash flows for periods prior to May 9, 2018. Our balance sheet as of September 30, 2018, reflects the consolidated balances of Apergy while the December 31, 2017, balance sheet reflects the combined balances of the Dover upstream oil and gas energy businesses that were transferred to Apergy. Our management believes the assumptions underlying these condensed consolidated financial statements, including the assumptions regarding the allocation of corporate expenses from Dover for periods prior to the Separation, are reasonable. The legal transfer of the upstream oil and gas energy businesses from Dover to Apergy occurred on May 9, 2018; however, for ease of reference, and unless otherwise stated or the context otherwise requires, all references to “Apergy Corporation,” “Apergy,” “we,” “us” or “our” refer (i) prior to the Separation, to the Apergy businesses, consisting of entities, assets and liabilities conducting the upstream oil and gas business within Dover’s Energy segment and (ii) after the Separation, to Apergy Corporation and its consolidated subsidiaries. Interim Financial Information The accompanying unaudited condensed consolidated financial statements of Apergy have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and pursuant to the rules and regulations of the SEC pertaining to interim financial information. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP have been condensed or omitted. Therefore, these financial statements should be read in conjunction with the audited combined financial statements, and notes thereto, in the Information Statement included in Amendment No. 1 to the Form 10 filed with the SEC on April 12, 2018. The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Although these estimates are based on management’s best knowledge of current events and actions that we may undertake in the future, actual results may differ from our estimates. In the opinion of management, the accompanying unaudited condensed consolidated financial statements reflect all adjustments (consisting of normal recurring adjustments unless otherwise specified) necessary for a fair statement of our financial condition and results of operations as of and for the periods presented. Revenue, expenses, assets and liabilities can vary during each quarter of the year. Therefore, the results and trends in these financial statements may not be representative of the results that may be expected for the year ending December 31, 2018.
Reclassifications	Reclassifications Beginning in the first quarter of 2018, we changed our presentation of expenditures related to purchases of leased assets. Previously, these amounts were reported in the operating section of our cash flow statement as “other” in adjustments to reconcile net income but are now reported as changes in our operating assets and liabilities in the operating section of our cash flow statement as “leased assets and other.” During the first quarter of 2018, we changed our presentation of amortization expense primarily related to customer intangible assets. For the three and nine months ended September 30, 2017, we reclassified $11.0 million and $32.1 million of amortization expense previously reported as a component of “selling, general and administrative expense” to “cost of goods and services” on our condensed combined statements of income. During the second quarter of 2018, we changed our presentation of capital lease obligations. As of December 31, 2017, we reclassified $3.7 million of capital lease obligations previously reported as “other long-term liabilities” to “long-term debt” on our condensed combined balance sheet. Certain prior-year amounts have been reclassified to conform to the current year presentation. See Note 2 — New Accounting Standards for additional information.	Reclassifications We changed our presentation of expenditures related to purchases of leased inventory. Previously, these amounts were reported in the operating section of our cash flow statement as “other” in adjustments to reconcile net income but are now reported as changes in our operating assets and liabilities in the operating section of our cash flow statement as “leased assets and other, net.” We changed our presentation of amortization expense primarily related to customer intangible assets. For the years ended December 31, 2017, 2016 and 2015, we reclassified $42.9 million, $45.2 million and $48.3 million of amortization expense previously reported as a component of “selling, general and administrative expense” to “cost of goods and services” on our combined statements of income. Certain amounts in prior years have been reclassified to conform to the current year presentation.
Recently Adopted and Issued Accounting Standards	Recently Adopted Accounting Standards Effective January 1, 2018, we early adopted Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) No. 2018-02, “ Income Statement — Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. Effective January 1, 2018, we adopted ASU 2017-07, Compensation — Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. non-operating non-operating Effective January 1, 2018, we adopted ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business Effective January 1, 2018, we adopted ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments.” Effective January 1, 2018, we adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606). During the second half of 2015, Dover developed a project plan to implement ASU 2014-09, We have applied the following practical expedients or elections under the new standard: • We elected to omit disclosure of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less and (ii) contracts for which we recognize revenue at the amount to which we have the right to invoice for services performed. • We applied the practical expedient to not capitalize costs to obtain contracts with a duration of one year or less, which are expensed and included within “cost of goods and services” in the condensed consolidated statements of income. • We elected to use the practical expedient to not adjust the promised amount of consideration for the effects of a significant financing component if it is expected, at contract inception, that the period between when we transfer a promised good or service to a customer, and when the customer pays for that good or service, will be one year or less. Thus, we may not consider an advance payment to be a significant financing component, if it is received less than one year before product completion. • We elected to exclude all taxes assessed by a governmental authority that are both imposed on and concurrent with a specific revenue-producing transaction and collected from a customer (e.g., sales, use, value added, and some excise taxes) from the determination of the transaction price. As a result, our accounting policy of reporting revenue net of these taxes was not changed under the new standard. • We elected to account for shipping and handling activities performed after control of a good has been transferred to the customer as a contract fulfillment cost. As a result, our accounting policy related to shipping and handling was not changed under the new standard. See Note 11 — Revenue for additional information. Recently Issued Accounting Standards In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) right-of-use catch-up After the Separation from Dover, we developed a project plan and established a cross-functional team to continue the process of implementing the new guidance, which included an evaluation of the work performed by Dover prior to the Separation. We made progress on our plan including gathering information on all leases, surveying our businesses, assessing our portolfio of leases and compiling a central repository of active leases. During the third quarter of 2018, we completed diagnostic reviews of certain sampled leases to support our policy elections. Additionally, we made significant progress configuring and implementing a new lease software system. We continue to evaluate our policy elections and considerations under the new lease guidance, including the potential use of practical expedients, and we are in the process of updating our internal control and business processes. As we continue to assess the impact the guidance will have on our financial statements and related disclosures, internal control over financial reporting and other business practices and processes, we expect to recognize right of use assets and liabilities for operating leases in our consolidated balance sheet upon adoption. In June 2016, the FASB issued ASU 2016-13, “ Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use 350-40): internal-use internal-use	Recent Accounting Pronouncements Recently Issued Accounting Standards The following standards, issued by the Financial Accounting Standards Board (“FASB”), will, or are expected to, result in a change in practice and/or have a financial impact to the Company’s Combined Financial Statements: In March 2017, the FASB issued Accounting Standards Update (“ASU”) 2017-07, In January 2017, the FASB issued ASU 2017-01, In February 2016, the FASB issued ASU 2016-02, After the Separation from Dover, we developed a project plan and established a cross-functional team to continue the process of implementing the new guidance, which included an evaluation of the work performed by Dover prior to the Separation. We made progress on our plan including gathering information on all leases, surveying our business, assessing our portfolio of leases and compiling a central repository of active leases. During the third quarter of 2018, we completed diagnostic reviews of certain sampled leases to support our policy elections. Additionally, we made significant progress configuring and implementing a new lease software system. We continue to evaluate our policy elections and considerations under the new lease guidance, including the potential use of practical expedients, and we are in the process of updating our internal control and business processes. As we continue to assess the impact the guidance will have on our financial statements and related disclosures, internal control over financial reporting and other business practices and processes, we expect to recognize right of use assets and liabilities for operating leases in our consolidated balance sheet upon adoption. In May 2014, the FASB issued ASU 2014-09, which the entity expects to be entitled, in exchange for those goods or services. This ASU also requires disclosures sufficient to enable users to understand the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers, including qualitative and quantitative disclosures about contracts with customers, significant judgments and changes in judgments and assets recognized from the costs to obtain or fulfill a contract. This guidance is effective for the Company on January 1, 2018. Dover commenced its assessment of ASU 2014-09 Recently Adopted Accounting Standards Effective January 1, 2018, we adopted ASU 2016-15, In January 2017, the FASB issued ASU 2017-04, In July 2015, the FASB issued ASU 2015-11,
Description of Business		Description of Business Apergy is a leading provider of highly engineered technologies that help companies drill for and produce oil and gas efficiently and safely around the world. Its products include a full range of equipment and technologies that enable efficient drilling and safe and efficient production throughout the lifecycle of a well. Its principal products consist of artificial lift equipment and solutions, including electric submersible pump systems (“ESP”), rod pumping systems (“Rod Lift”), gas lift systems, progressive cavity pump systems (“PCP”) and plunger lift systems, as well as polycrystalline diamond cutters (“PDCs”) for drilling. The Company also provides a comprehensive automation offering consisting of equipment, software and Industrial Internet (“IIoT”) solutions for downhole monitoring, wellsite productivity enhancement and asset integrity management. The Company reports two business segments: Production & Automation Technologies and Drilling Technologies. For additional information on the Company’s segments, see Note 16 — Segment Information. In 2017, the Company acquired PCP Oil Tools S.A. and Ener Tools S.A., a supplier of progressive cavity pump products and services. This acquisition is part of the Production & Automation Technologies segment. Additionally, the Company did not make any acquisitions during the years ended December 31, 2016 and 2015.
Combined Financial Statement Presentation		Combined Financial Statement Presentation The Combined Financial Statements have been derived from the consolidated financial statements and accounting records of Dover using the historical results of operations, and historical basis of assets and liabilities of Apergy and reflect Dover’s net investment in Apergy. Historically, stand-alone financial statements have not been prepared for Apergy. Management believes the assumptions underlying the allocations included in the Combined Financial Statements are reasonable. However, the Combined Financial Statements may not necessarily reflect Apergy’s results of operations, financial position and cash flows in the future, or what Apergy’s results of operations, financial position and cash flows would have been had Apergy been a stand-alone company during the periods presented herein. The Combined Financial Statements include the accounts of the Company. Intercompany accounts and transactions have been eliminated in consolidation. The results of operations of purchased businesses of Apergy are included from the date of acquisition. The accompanying financial statements include allocations of costs that were incurred by Dover for functions such as corporate executive management, human resources, information technology, facilities, tax, shared services, finance and legal, including the costs of salaries, benefits and other related costs. The total costs allocated to the accompanying Combined Financial Statements for these functions totaled approximately $22,987, $19,459 and $20,852 for the years ended December 31, 2017, 2016 and 2015, respectively, and are included in Selling, general and administrative expenses within the Combined Statements of Income. These expenses have been allocated to Apergy based on direct usage or benefit where identifiable, with the remainder allocated on the basis of revenues, headcount, or other measures. As a stand-alone public company, Apergy’s total costs related to such support functions may differ from the costs that were historically allocated to it from Dover. See Note 3 — Related Party Transactions for additional information regarding related party transactions.
Use of Estimates		Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the Combined Financial Statements and accompanying disclosures. These estimates may be adjusted due to changes in future economic, industry, or customer financial conditions, as well as changes in technology or demand. Estimates are used for, but not limited to, allowances for doubtful accounts receivable, net realizable value of inventories, restructuring reserves, warranty reserves, pension and post-retirement plans, stock-based compensation, useful lives for depreciation and amortization of long-lived assets, future cash flows associated with impairment testing for goodwill, indefinite-lived intangible assets and other long-lived assets, deferred tax assets, uncertain income tax positions and contingencies. Actual results may ultimately differ from estimates, although management does not believe such differences would materially affect the Combined Financial Statements in any individual year. Estimates and assumptions are periodically reviewed and the effects of revisions are reflected in the Combined Financial Statements in the period that they are determined.
Cash and Cash Equivalents		Cash and Cash Equivalents Cash and cash equivalents include cash on hand, demand deposits and short-term investments which are highly liquid in nature and have original maturities at the time of purchase of three months or less. The carrying value of cash and cash equivalents approximate fair value.
Accounts Receivable and Allowance for Doubtful Accounts		Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable are recorded at face amounts less an allowance for doubtful accounts. The allowance is an estimate based on historical collection experience, current economic and market conditions and a review of the current status of each customer’s trade accounts receivable. Management evaluates the aging of the accounts receivable balances and the financial condition of its customers to estimate the amount of accounts receivable that may not be collected in the future and records the appropriate provision.
Inventories		Inventories Inventories for the majority of the Company’s subsidiaries, including all international subsidiaries, are stated at the lower of net realizable value, determined on the first-in, first-out
Property, Plant and Equipment		Property, Plant and Equipment Property, plant and equipment includes the historical cost of land, buildings, machinery and equipment, purchased software and significant improvements to existing plant and equipment or, in the case of acquisitions, a fair market value appraisal of assets. Expenditures for maintenance, repairs and minor renewals are expensed as incurred. When property or equipment is sold or otherwise disposed of, the related cost and accumulated depreciation is removed from the respective accounts and the gain or loss realized on disposition is reflected in earnings. The Company depreciates its assets on a straight-line basis over their estimated useful lives as follows: buildings and improvements 5 to 31.5 years; machinery and equipment 3 to 7 years; furniture and fixtures 3 to 7 years; vehicles 3 years; and software 3 to 10 years.
Derivative Financial Instruments		Derivative Financial Instruments The Company uses derivative financial instruments to hedge its exposure to foreign currency exchange rate risk. The Company does not enter into derivative financial instruments for speculative purposes and has a portfolio of derivatives that is not material in value. Derivative financial instruments used for hedging purposes must be designated and effective as a hedge of the identified risk exposure at inception of the contract. For derivatives hedging the fair value of assets or liabilities, the changes in fair value of both the derivatives and of the hedged items are recorded in current earnings.
Goodwill, Other Intangible Assets and Long-Lived Assets		Goodwill, Other Intangible Assets and Long-Lived Assets Goodwill represents the excess of purchase price over the fair value of net assets acquired. Goodwill and certain other intangible assets deemed to have indefinite lives (trademarks) are not amortized. For goodwill, impairment tests are required at least annually, or more frequently if events or circumstances indicate that it may be impaired, or when some portion but not all of a reporting unit is disposed. Historically, the Company was part of the Dover Energy operating segment. Based on its historical organizational structure, the Company identified two reporting units for which cash flows are determinable and to which goodwill may be allocated. Effective in the fourth quarter of 2017, the Company determined it is organized into a new segment structure discussed in Note 16 — Segment Information comprised of two reporting units, to which goodwill may be allocated. The Company performs its goodwill impairment test annually in the fourth quarter at the reporting unit level. A quantitative test is used to determine existence of goodwill impairment and the amount of the impairment loss at the reporting unit level. The quantitative test compares the fair value of a reporting unit with its carrying amount, including goodwill. The Company uses an income-based valuation method, determining the present value of estimated future cash flows, to estimate the fair value of a reporting unit. If the fair value of a reporting unit exceeds its carrying amount, goodwill of the reporting unit is not impaired. If the carrying amount of a reporting unit exceeds its fair value, an impairment loss shall be recognized in an amount equal to that excess, limited to the total amount of goodwill allocated to that reporting unit. Factors used in the impairment analysis require significant judgment, and actual results may differ from assumed and estimated amounts. The Company uses its own market assumptions including internal projections of future cash flows, discount rates and other assumptions considered reasonable and inherent in the analysis. These forecasts are based on historical performance and future estimated results. The discount rates used in these analyses vary by reporting unit and are based on a capital asset pricing model and published relevant industry rates. The Company uses discount rates commensurate with the risks and uncertainties inherent to each reporting unit and in the internally developed forecasts. See Note 7 — Goodwill and Other Intangible Assets for further discussion of the Company’s annual goodwill impairment test and results. The Company uses an income-based valuation method to test its indefinite-lived intangible assets for impairment, at least annually. The fair value of the intangible asset is compared to its carrying value. This method uses the Company’s own market assumptions considered reasonable and inherent in the analysis. Any excess of carrying value over the estimated fair value is recognized as an impairment loss. No impairment of indefinite-lived intangible assets was required for the years ended December 31, 2017, 2016 and 2015. Other intangible assets with determinable lives consist primarily of customer intangibles, unpatented technologies, patents and trademarks. These other intangibles are amortized over their estimated useful lives, ranging from 5 to 15 years. Long-lived assets (including definite-lived intangible assets) are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable, such as a significant sustained change in the business climate. If an indicator of impairment exists for any grouping of assets, an estimate of undiscounted future cash flows is produced and compared to its carrying value. If an asset is determined to be impaired, the loss is measured by the excess of the carrying amount of the asset over its fair value as determined by an estimate of discounted future cash flows.
Restructuring Accruals		Restructuring Accruals From time to time, the Company takes actions to reduce headcount, close facilities, or otherwise exit operations. Such restructuring activities at an operation are recorded when management has committed to an exit or reorganization plan and when termination benefits are probable and can be reasonably estimated based on circumstances at the time the restructuring plan is approved by management or when termination benefits are communicated. Exit costs include future minimum lease payments on vacated facilities and other contractual terminations. In addition, asset impairments may be recorded as a result of an approved restructuring plan. The accrual of both severance and exit costs requires the use of estimates. Though the Company believes that its estimates accurately reflect the anticipated costs, actual results may differ from the original estimated amounts.
Noncontrolling interests		Noncontrolling interests A noncontrolling interest represents the equity interest in a subsidiary that is not attributable, either directly or indirectly, to the Company and is reported as equity, separately from the Company’s controlling interests. The noncontrolling interest relates to the Company’s ownership interest in Norris Production Solutions Middle East LLC, a subsidiary company in the Sultanate of Oman with a local partner, where the Company is the majority owner at 60% and has the controlling financial interest. The outside investor’s interests in this subsidiary company are included in noncontrolling interest in the Company’s Combined Financial Statements.
Foreign Currency		Foreign Currency Assets and liabilities of non-U.S. subsidiaries, where the functional currency is not the U.S. dollar, have been translated at year-end exchange rates and profit and loss accounts have been translated using weighted-average monthly exchange rates. Foreign currency translation gains and losses are included in the Combined Statements of Comprehensive Income as a component of Other comprehensive income (loss). Assets and liabilities of an entity that are denominated in currencies other than an entity’s functional currency are re-measured into the functional currency using end of period exchange rates or historical rates where applicable to certain balances. Gains and losses related to these re-measurements are recorded within the Combined Statements of Income as a component of Other expense, net.
Revenue Recognition		Revenue Recognition Revenue is recognized when all of the following conditions are satisfied: a) persuasive evidence of an arrangement exists, b) price is fixed or determinable, c) collectability is reasonably assured and d) delivery has occurred or services have been rendered. The majority of the Company’s revenue is generated through the manufacture and sale of a broad range of specialized products and components, with revenue recognized upon transfer of title and risk of loss, which is generally upon shipment. Certain product sales are recognized based on the percentage-of-completion In limited cases, revenue arrangements with customers require delivery, installation, testing, or other acceptance provisions to be satisfied before revenue is recognized. The Company includes shipping costs billed to customers in revenue and the related shipping costs in cost of goods and services.
Stock-Based Compensation		Stock-Based Compensation The Company’s employees have historically participated in Dover’s stock-based compensation plans. Stock-based compensation has been allocated to the Company based on the awards and terms previously granted to the Company’s employees. The principal awards issued under the stock-based compensation plans include stock options, stock-settled stock appreciation rights, restricted stock units and performance share awards. The cost of such awards is measured at the grant date based on the fair value of the award. At the time of grant, Dover estimates forfeitures, based on historical experience, in order to estimate the portion of the award that will ultimately vest. The value of the portion of the award that is expected to ultimately vest is recognized as expense on a straight-line basis, generally over the explicit service period of three years (except for retirement-eligible employees and retirees) and is included in Selling, general and administrative expenses in the Combined Statements of Income. Expense for awards granted to retirement-eligible employees is recorded over the period from the date of grant through the date the employee first becomes eligible to retire and is no longer required to provide service. See Note 12 — Equity and Cash Incentive Program for additional information related to stock-based compensation.
Employee Benefit Plans		Employee Benefit Plans Apergy participates in defined benefit plans and non-qualified supplemental retirement plans sponsored by Dover that are accounted for as multi-employer plans in the Combined Financial Statements. Apergy also sponsors a defined benefit plan and non-qualified plan. These plans are accounted for as single employer plans in the Combined Financial Statements. Apergy also offers a defined contribution plan. See Note 14 — Employee Benefit Plans and Non-Qualified Plans for additional information.
Income Taxes		Income Taxes The Company’s operations have historically been included in Dover’s consolidated federal tax return and certain combined state returns. The income tax expense in these Combined Financial Statements has been determined on a stand-alone return basis in accordance with Accounting Standards Codification (“ASC”) 740 “Income Taxes,” which requires the recognition of income taxes using the liability method. Under this method, the Company is assumed to have historically filed a return separate from Dover, reporting its taxable income or loss and paying applicable tax based on its separate taxable income and associated tax attributes in each tax jurisdiction. Income taxes payable at each balance sheet date computed under the stand-alone return basis are classified within Parent Company investment in Apergy since Dover is legally liable for the tax. Accordingly, changes in income taxes payable are recorded as a component of financing activities in the Combined Statements of Cash Flows. The calculation of income taxes on the separate return basis requires considerable judgment and the use of both estimates and allocations. As a result, the Company’s effective tax rate and deferred tax balances will differ significantly from those in Dover’s historic periods. Additionally, the Company’s deferred tax balances as calculated on the separate return basis will differ from the deferred tax balances of Dover, if legally separated. See Note 11 — Income Taxes for additional information on the Company’s income taxes and unrecognized tax benefits. The U.S. bill commonly referred to as the Tax Cuts and Jobs Act (“Tax Reform Act”), which was enacted on December 22, 2017, significantly changes U.S. tax law by, among other things, lowering corporate income tax rates, implementing a territorial tax system and imposing a repatriation tax on deemed repatriated earnings of foreign subsidiaries. The Tax Reform Act permanently reduces the U.S. corporate income tax rate from a maximum of 35% to a flat 21% rate, effective January 1, 2018. The Tax Reform Act also provided for a one-time deemed repatriation of post-1986 undistributed foreign subsidiary earnings and profits through the year ended December 31, 2017. The Global Intangible Low-Taxed Income (“GILTI”) provisions require the Company to include in its U.S. income tax return foreign subsidiary earnings in excess of an allowable return on the foreign subsidiary’s tangible assets. The Company expects that it will be subject to incremental U.S. tax on GILTI income beginning in 2018, due to expense allocations required by the U.S. foreign tax credit rules. The Company has elected to account for GILTI tax in the period in which it is incurred, and therefore has not provided any deferred tax impacts of GILTI in its combined financial statements for the year ended December 31, 2017. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118 (“SAB 118”) to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Reform Act. The Company has recognized the provisional tax impacts related to deemed repatriated earnings and the benefit for the revaluation of deferred tax assets and liabilities, and included these amounts in its combined financial statements for the year ended December 31, 2017. The final impact may differ from these provisional amounts, possibly materially, due to, among other things, additional analysis, changes in interpretations and assumptions the Company has made, additional regulatory guidance that may be issued, and actions the Company may take as a result of the Tax Reform Act. In accordance with SAB 118, the financial reporting impact of the Tax Reform Act will be completed in the fourth quarter of 2018.
Research and Development Costs		Research and Development Costs Research and development costs, including qualifying engineering costs, are expensed when incurred and amounted to $18,501, $16,511 and $19,255, in 2017, 2016 and 2015, respectively.
Advertising Costs		Advertising Costs Advertising costs are expensed when incurred and amounted to $1,220, $825 and $1,604, in 2017, 2016 and 2015, respectively.
Risk, Retention, Insurance		Risk, Retention, Insurance Apergy was covered under Dover’s insurance policies during the years ended December 31, 2017 and 2016. For both years ended December 31, 2017 and 2016, Dover self-insured its product and commercial general liability claims up to $5.0 million per occurrence and automobile liability claims up to $1.0 million per occurrence. For the years ended December 31, 2017 and 2016, Dover self-insured its workers’ compensation claims up to $0.8 million per occurrence, respectively. Third-party insurance provides primary level coverage in excess of these amounts up to certain specified limits. In addition, Dover has excess liability insurance from third-party insurers on both an aggregate and an individual occurrence basis well in excess of the limits of the primary coverage. A worldwide program of property insurance covers Dover’s owned and leased property and any business interruptions that may occur due to an insured hazard affecting those properties, subject to reasonable deductibles and aggregate limits. Dover’s property and casualty insurance programs contain various deductibles that, based on Dover’s experience, are typical and customary for a company of its size and risk profile. Apergy does not consider any of the deductibles under the Dover program to represent a material risk to Apergy. Dover generally maintains deductibles for claims and liabilities related primarily to workers’ compensation, health and welfare claims, general commercial, product and automobile liability and property damage and business interruption resulting from certain events. Dover accrues for claim exposures that are probable of occurrence and can be reasonably estimated. As part of Dover’s risk management program, insurance is maintained to transfer risk beyond the level of self-retention and provide protection on both an individual claim and annual aggregate basis.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule of earnings per share, basic and diluted	A reconciliation of the number of shares used for the basic and diluted earnings per share calculation was as follows: Three Months Ended Nine Months Ended (in thousands, except per share data) 2018 2017 2018 2017 Net income attributable to Apergy $ 25,263 $ 18,421 $ 71,989 $ 50,444 Weighted-average number of shares outstanding 77,340 77,340 77,340 77,340 Dilutive effect of stock-based compensation 229 550 402 550 Total shares and dilutive securities 77,569 77,890 77,742 77,890 Basic earnings per share attributable to Apergy $ 0.33 $ 0.24 $ 0.93 $ 0.65 Diluted earnings per share attributable to Apergy $ 0.33 $ 0.24 $ 0.93 $ 0.65

Inventories (Tables)

Inventories (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Inventory, Net [Abstract]
Components of Inventories	Inventories consisted of the following: (in thousands) September 30, December 31, Raw materials $ 48,735 $ 45,408 Work in progress 11,130 10,879 Finished goods 184,871 167,416 244,736 223,703 LIFO and valuation adjustments (25,603 ) (22,112 ) Inventories, net $ 219,133 $ 201,591	The components of inventories were as follows: December 31, December 31, Raw materials $ 45,408 $ 45,209 Work in progress 10,879 10,321 Finished goods 167,416 153,040 Subtotal 223,703 208,570 Less reserves (22,112 ) (24,012 ) Total $ 201,591 $ 184,558

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Components of property, plant and equipment, net	Property, plant and equipment consisted of the following: (in thousands) September 30, December 31, Land $ 13,623 $ 13,557 Buildings and improvements 104,026 99,233 Machinery, equipment and other 501,148 446,261 618,797 559,051 Accumulated depreciation (382,730 ) (347,219 ) Property, plant and equipment, net $ 236,067 $ 211,832	The components of property, plant and equipment, net were as follows: December 31, December 31, Land $ 13,557 $ 14,636 Buildings and improvements 99,233 91,927 Machinery, equipment and other 446,261 396,505 Property, plant and equipment, gross 559,051 503,068 Total accumulated depreciation (347,219 ) (301,321 ) Property, plant and equipment, net $ 211,832 $ 201,747

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	The carrying amount, including changes therein, of goodwill by reporting segment was as follows: (in thousands) Production & Drilling Total December 31, 2017 $ 808,952 $ 101,136 $ 910,088 Purchase price adjustment * (53 ) — (53 ) Foreign currency translation (3,269 ) — (3,269 ) September 30, 2018 $ 805,630 $ 101,136 $ 906,766 * Purchase price adjustment related to our 2017 acquisition of PCP Oil Tools S.A. and Ener Tools S.A.	The changes in the carrying value of goodwill by operating segment were as follows: Production & Drilling Total Balance at December 31, 2015 $ 800,792 $ 101,136 $ 901,928 Foreign currency translation 651 — 651 Balance at December 31, 2016 801,443 101,136 902,579 Acquisitions 5,053 — 5,053 Foreign currency translation 2,456 — 2,456 Balance at December 31, 2017 $ 808,952 $ 101,136 $ 910,088
Schedule of Intangible Assets	The components of our definite- and indefinite-lived intangible assets were as follows: September 30, 2018 December 31, 2017 (in thousands) Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Definite-lived intangible assets: Customer intangibles $ 569,832 $ 309,355 $ 260,477 $ 572,415 $ 276,655 $ 295,760 Trademarks 36,307 20,648 15,659 36,312 17,821 18,491 Patents 38,514 22,959 15,555 38,679 20,449 18,230 Unpatented technologies 9,700 9,700 — 9,700 9,700 — Drawings and manuals 3,047 2,163 884 3,067 2,109 958 Other 5,346 4,124 1,222 5,382 3,911 1,471 662,746 368,949 293,797 665,555 330,645 334,910 Indefinite-lived intangible assets: Trademarks 3,600 — 3,600 3,600 — 3,600 Total $ 666,346 $ 368,949 $ 297,397 $ 669,155 $ 330,645 $ 338,510	The following table provides the gross carrying value and accumulated amortization for each major class of intangible assets: December 31, 2017 December 31, 2016 Gross Amount Accumulated Amortization Net Gross Amount Accumulated Amortization Net Amortized intangible assets: Customer Intangibles $ 572,415 $ 276,655 $ 295,760 $ 566,602 $ 229,902 $ 336,700 Trademarks 36,312 17,821 18,491 36,296 14,013 22,283 Patents 38,679 20,449 18,230 38,106 16,662 21,444 Unpatented Technologies 9,700 9,700 — 9,700 9,700 — Drawings & Manuals 3,067 2,109 958 3,001 1,942 1,059 Other 5,382 3,911 1,471 5,270 3,539 1,731 Total amortized intangibles 665,555 330,645 334,910 658,975 275,758 383,217 Unamortized intangible assets: Trademarks 3,600 — 3,600 3,600 — 3,600 Total intangible assets $ 669,155 $ 330,645 $ 338,510 $ 662,575 $ 275,758 $ 386,817
Estimated Future Amortization Expense related to Intangible Assets		Estimated future amortization expense related to intangible assets held at December 31, 2017 is as follows: Estimated 2018 $ 52,357 2019 51,509 2020 50,059 2021 49,231 2022 47,683

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Schedule of Debt	Long-term debt consisted of the following: (in thousands) September 30, December 31, Revolving credit facility $ — $ — Term loan facility 395,000 — 6.375% Senior Notes due 2026 300,000 — Capital leases 4,337 3,742 Total 699,337 3,742 Net unamortized discounts and issuance costs (11,794 ) — Total long-term debt $ 687,543 $ 3,742

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Accumulated Other Comprehensive Loss	Accumulated other comprehensive loss consisted of the following: (in thousands) Foreign Currency Defined Pension and Accumulated Other December 31, 2017 $ (21,935 ) $ (4,480 ) $ (26,415 ) Reclassification adjustment for cumulative effect of change in accounting principle — (1,315 ) (1,315 ) Net transfer from Dover Corporation — (2,421 ) (2,421 ) Other comprehensive income (loss) before reclassifications, net of tax (9,080 ) 170 (8,910 ) Reclassification adjustment for net losses (gains) included in net income, net of tax — 534 534 Other comprehensive income (loss), (9,080 ) 704 (8,376 ) September 30, 2018 $ (31,015 ) $ (7,512 ) $ (38,527 )	The components of Accumulated other comprehensive (loss) income are as follows: December 31, December 31, Cumulative foreign currency translation adjustments $ (21,935 ) $ (26,293 ) Pension and other post-retirement benefit plans (4,480 ) (7,336 ) $ (26,415 ) $ (33,629 )
Reclassification from Accumulated Other Comprehensive Income (Loss)	Reclassification adjustments from accumulated other comprehensive loss to net income related to defined pension and other post-retirement benefits consisted of the following: Three Months Ended Nine Months Ended Affected line items on the (in thousands) 2018 2017 2018 2017 Amortization of actuarial loss (1) $ 116 $ 100 $ 243 $ 299 Other expense, net Settlement loss (1) 484 — 484 — Selling, general and administrative expense Total before tax 600 100 727 299 Income before income taxes Tax benefit (161 ) (35 ) (192 ) (102 ) Provision for income taxes $439 $65 $535 $197 Net income (1) These accumulated comprehensive loss components are included in the computation of net periodic benefit cost (See Note16—Employee Benefit Plans for additional information).	Amounts reclassified from Accumulated other comprehensive income (loss) to income (loss) during the year ended December 31, 2017, 2016 and 2015 were as follows: Years Ended December 31, 2017 2016 2015 Pension and other post-retirement benefit plans: Amortization of actuarial losses and net transition obligation $ 397 $ 362 $ 340 Amortization of prior service costs 2 2 2 Total before tax 399 364 342 Tax benefit (141 ) (129 ) (120 ) Net of tax $ 258 $ 235 $ 222
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)		The amounts recognized in Other comprehensive income (loss) were as follows: Year Ended December 31, 2017 Pre-tax Tax Net of tax Foreign currency translation adjustments $ 4,358 $ — $ 4,358 Pension and other post-retirement benefit plans 3,827 (971 ) 2,856 Total other comprehensive income (loss) $ 8,185 $ (971 ) $ 7,214 Year Ended December 31, 2016 Pre-tax Tax Net of tax Foreign currency translation adjustments $ 953 $ — $ 953 Pension and other post-retirement benefit plans 154 (42 ) 112 Total other comprehensive income (loss) $ 1,107 $ (42 ) $ 1,065 Year Ended December 31, 2015 Pre-tax Tax Net of tax Foreign currency translation adjustments $ (11,691 ) $ — $ (11,691 ) Pension and other post-retirement benefit plans (393 ) 124 (269 ) Total other comprehensive (loss) income $ (12,084 ) $ 124 $ (11,960 )
Schedule of Comprehensive Income (Loss)		Total Comprehensive income (loss) were as follows: Years Ended December 31, 2017 2016 2015 Net income (loss) attributable to Apergy $ 110,638 $ (12,642 ) $ 51,698 Other comprehensive income (loss) 7,214 1,065 (11,960 ) Comprehensive income (loss) $ 117,852 $ (11,577 ) $ 39,738

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	Revenue disaggregated by end market in each of our reporting segments was as follows: (in thousands) Three Months Ended Nine Months Drilling Technologies $ 75,254 $ 209,727 Production & Automation Technologies: Artificial lift 188,005 544,566 Digital products 31,114 85,347 Other production equipment 22,380 68,922 Intra-segment eliminations (285 ) (2,244 ) 241,214 696,591 Total revenue $ 316,468 $ 906,318 Revenue disaggregated by geography was as follows: (in thousands) Three Months Ended Nine Months Ended United States $ 252,747 $ 713,373 Canada 20,759 58,639 Middle East 13,645 40,091 Europe 7,625 27,805 Latin America 8,364 25,097 Asia-Pacific 3,715 13,900 Other 9,613 27,413 Total revenue $ 316,468 $ 906,318
Schedule of Contract Balances	Contract assets and contract liabilities from contracts with customers were as follows: (in thousands) September 30, 2018 January 1, 2018 Contract assets $ 3,475 $ 4,733 Contract liabilities — current 6,827 4,487

Restructuring and Other Relat_2

Restructuring and Other Related Charges (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Schedule of Restructuring and Related Costs	Restructuring and other related charges as classified in our condensed consolidated statements of income were as follows: Three Months Ended Nine Months Ended (in thousands) 2018 2017 2018 2017 Cost of goods and services $ (33 ) $ (16 ) $ 1,557 $ (17 ) Selling, general and administrative expense (6 ) 24 916 38 Total $ (39 ) $ 8 $ 2,473 $ 21	The Company initiated various restructuring programs and incurred severance and other restructuring costs by segment as follows: Years Ended December 31, 2017 2016 2015 Production & Automation Technologies $ 6,921 $ 12,757 $ 18,750 Drilling Technologies — 2,405 2,480 Total $ 6,921 $ 15,162 $ 21,230 These amounts are classified in the Combined Statements of Income as follows: Cost of goods and services $ 6,332 $ 9,465 $ 9,095 Selling, general and administrative expenses 589 5,697 12,135 Total $ 6,921 $ 15,162 $ 21,230
Schedule of Restructuring Accruals Activities		The following table details the Company’s severance and other restructuring accrual activities: Severance Exit Total Balance at December 31, 2014 $ 95 $ — $ 95 Restructuring charges 9,366 11,864 21,230 Payments (8,197 ) (3,947 ) (12,144 ) Other, including foreign currency translation (1) (100 ) (7,194 ) (7,294 ) Balance at December 31, 2015 1,164 723 1,887 Restructuring charges 10,496 4,666 15,162 Payments (11,235 ) (2,410 ) (13,645 ) Other, including foreign currency translation (1) (175 ) (2,770 ) (2,945 ) Balance at December 31, 2016 $ 250 $ 209 $ 459 Restructuring charges 151 6,770 6,921 Payments (400 ) (978 ) (1,378 ) Other, including foreign currency translation (1) (1 ) (3,450 ) (3,451 ) Balance at December 31, 2017 $ — $ 2,551 $ 2,551 (1) Other activity in exit reserves primarily represents the non-cash write-off

Equity and Cash Incentive Pro_2

Equity and Cash Incentive Program (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Share Based Compensation Abstract
Schedule of Stock-Based Compensation Expense	Stock-based compensation expense relating to all stock-based incentive plans was as follows: Three Months Ended Nine Months Ended 2018 2017 2018 2017 Stock-based compensation expense $ 1,768 $ 630 $ 3,129 $ 1,762 Tax benefit (421 ) (219 ) (717 ) (611 ) Stock-based compensation expense, net of tax $ 1,347 $ 411 $ 2,412 $ 1,151	The following table summarizes the Company’s compensation expense relating to all stock-based incentive plans: Years Ended December 31, 2017 2016 2015 Pre-tax $ 2,236 $ 2,293 $ 1,925 Tax benefit (774 ) (787 ) (658 ) Total stock-based compensation expense, net of tax $ 1,462 $ 1,506 $ 1,267
Schedule of Assumptions used for calculating fair value of SAR granted		The fair value of each SAR granted was estimated on the date of grant using a Black-Scholes option-pricing model with the following assumptions: 2017 2016 2015 Risk-free interest rate 1.80 % 1.05 % 1.51 % Dividend yield 2.27 % 3.09 % 2.24 % Expected life (years) 4.6 4.6 5.1 Volatility 21.90 % 26.17 % 27.19 % Grant price $ 79.28 $ 57.25 $ 73.28 Fair value at date of grant $ 12.63 $ 9.25 $ 14.55
Summary of activity relating to SARs granted		A summary of activity relating to SARs granted under the Dover plans for the year ended December 31, 2017 is as follows: SARs Number Weighted Weighted Outstanding at January 1, 2017 454,683 $ 63.69 Granted 82,240 79.28 Forfeited / expired (32,944 ) 67.10 Exercised (116,908 ) 61.93 Outstanding at December 31, 2017 387,071 67.17 6.7 Exercisable at December 31, 2017 157,078 $ 64.30 4.6
Summary of outstanding SARs		The following table summarizes information about outstanding SARs at December 31, 2017: SARs Outstanding SARs Exercisable Range of Exercise Number Weighted Exercise Weighted Remaining in Years Aggregate Number Weighted Exercise Weighted Remaining in Years Aggregate $ 25.96 - $37.79 23,816 $ 37.79 2.1 $ 1,505 23,816 $ 37.79 2.1 $ 1,505 $ 40.54 - $58.69 125,469 $ 57.52 6.7 5,454 38,309 $ 58.14 3.6 1,642 $ 63.33 - $82.51 237,786 $ 75.21 7.2 6,130 94,953 $ 73.44 5.7 2,616 387,071 $ 13,089 157,078 $ 5,763
Other information regarding exercise of SARs and stock options		Other information regarding the exercise of SARs and stock options is listed below: 2017 2016 2015 SARs Fair value of SARs that became exercisable $ 1,239 $ 1,564 $ 1,356 Aggregate intrinsic value of SARs exercised $ 2,787 $ 799 $ 1,874 Stock Options Cash received by Dover for exercise of stock options $ — $ — $ 100 Aggregate intrinsic value of options exercised $ — $ — $ 117
Fair value used in determining compensation cost of Performance shares		The fair value and average attainment used in determining compensation cost of the performance shares issued in 2017, 2016 and 2015 are as follows for the year ended December 31, 2017: Performance shares 2017 2016 2015 Fair value per share at date of grant $ 79.28 $ 57.25 $ 73.28 Average attainment rate reflected in expense 0.0 % 0.0 % 0.0 %
Summary of activity for performance share awards		A summary of activity for performance share awards for the year ended December 31, 2017 is as follows: Number Weighted Grant-Date Fair Value Unvested at January 1, 2017 10,267 $ 64.28 Granted 4,162 79.28 Vested (4,503 ) 73.28 Unvested at December 31, 2017 9,926 $ 66.49
Summary of activity for restricted stock units		A summary of activity for restricted stock units for the year ended December 31, 2017 is as follows: Number Weighted Grant-Date Fair Value Unvested at January 1, 2017 54,064 $ 61.68 Granted 25,557 79.28 Forfeited (8,854 ) 64.07 Vested (20,712 ) 64.85 Unvested at December 31, 2017 50,055 $ 68.91

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Segment Reporting [Abstract]
Segment revenue and operating profit	Segment revenue and segment operating profit were as follows: Three Months Ended Nine Months Ended (in thousands) 2018 2017 2018 2017 Segment revenue: Production & Automation Technologies $ 241,214 $ 199,454 $ 696,591 $ 578,429 Drilling Technologies 75,254 59,200 209,727 166,664 Total revenue $ 316,468 $ 258,654 $ 906,318 $ 745,093 Income before income taxes: Segment operating profit: Production & Automation Technologies $ 24,257 $ 8,403 $ 57,957 $ 26,247 Drilling Technologies 26,209 20,420 71,738 55,067 Total segment operating profit 50,466 28,823 129,695 81,314 Corporate expense and other (1) 6,664 1,818 16,274 6,838 Interest expense, net 10,584 79 16,813 199 Income before income taxes $ 33,218 $ 26,926 $ 96,608 $ 74,277 (1) Corporate expense includes costs not directly attributable or allocated to our reporting segments such as corporate executive management and other administrative functions, costs related to our Separation from Dover Corporation and the results attributable to our noncontrolling interest.	Segment financial information and a reconciliation of segment results to combined results follows: Years Ended December 31, 2017 2016 2015 Revenue: Production & Automation Technologies $ 781,938 $ 638,017 $ 912,383 Drilling Technologies 227,653 113,320 164,297 Total combined revenue $ 1,009,591 $ 751,337 $ 1,076,680 Segment Income: Segment operating profit (loss) (1) Production & Automation Technologies (2) $ 24,889 $ (21,687 ) $ 58,446 Drilling Technologies 74,317 8,397 26,819 Total segment operating profit (loss) 99,206 (13,290 ) 85,265 Corporate expense / other (3) (10,852 ) (7,395 ) (9,436 ) Net income attributable to noncontrolling interest 930 1,851 1,436 Income (Loss) before income taxes $ 89,284 $ (18,834 ) $ 77,265 Depreciation and amortization: Production & Automation Technologies (4) $ 99,929 $ 99,607 $ 103,612 Drilling Technologies (5) 11,950 12,448 16,380 Combined total $ 111,879 $ 112,055 $ 119,992 Restructuring charges: Production & Automation Technologies $ 6,921 $ 12,757 $ 18,750 Drilling Technologies — 2,405 2,480 Combined total $ 6,921 $ 15,162 $ 21,230 Capital expenditures: Production & Automation Technologies $ 18,517 $ 21,588 $ 19,272 Drilling Technologies 8,171 4,137 4,945 Combined total $ 26,688 $ 25,725 $ 24,217 (1) Segment operating profit (loss) includes certain corporate expenses that are allocated to the segments such as information technology, supply chain, and shared services based on direct benefit where identifiable or other methods which the Company believes to be a reasonable reflection of the utilization of services provided. (2) Segment operating profit (loss) for Production & Automation Technologies excludes the net income attributable to noncontrolling interest. (3) Corporate expenses include those costs not attributable to a particular business segment such as corporate executive management and other corporate administrative functions. (4) Depreciation and amortization expense for Production & Automation Technologies includes acquisition-related depreciation and amortization of $57,426, $60,025 and $63,217 for the years ended December 31, 2017, 2016 and 2015, respectively. (5) Depreciation and amortization expense for Drilling Technologies includes acquisition-related depreciation and amortization of $24, $115 and $3,010 for the years ended December 31, 2017, 2016 and 2015, respectively. Total assets at December 31: 2017 2016 Production & Automation Technologies $ 1,683,782 $ 1,659,711 Drilling Technologies 220,993 191,184 Combined total $ 1,904,775 $ 1,850,895
Schedule of Revenue Classified by Significant Products and Services		Revenue classified by significant products and services were as follows: Years Ended December 31, 2017 2016 2015 Revenue: Artificial lift technologies $ 601,412 $ 499,033 $ 693,311 Automation technologies 82,093 65,351 93,639 Other production equipment 103,564 75,182 126,870 Drilling technologies 227,653 113,320 164,297 Intercompany eliminations (5) (5,131 ) (1,549 ) (1,437 ) Combined total $ 1,009,591 $ 751,337 $ 1,076,680 (5) Intercompany eliminations for the years ended December 31, 2017, 2016 and 2015 relate principally between the product groups automation technologies and artificial lift technologies.
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas		Information concerning principal geographic areas is presented as follows: Revenue Long-Lived Assets Years Ended December 31, At December 31, 2017 2016 2015 2017 2016 United States $ 769,928 $ 559,266 $ 808,549 $ 198,178 $ 184,268 Middle East 48,899 54,767 69,951 5,189 8,417 Canada 79,186 54,714 64,961 7,587 8,214 Europe 28,112 19,935 34,970 — — Australia 23,667 18,177 47,811 681 619 Latin & South America 34,368 23,588 23,208 197 229 Other 25,431 20,890 27,230 — — Combined total $ 1,009,591 $ 751,337 $ 1,076,680 $ 211,832 $ 201,747

Condensed Consolidating Finan_2

Condensed Consolidating Financial Information (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Condensed Balance Sheets	September 30, 2018 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Assets Cash and cash equivalents $ 108 $ 8,308 $ 9,598 $ — $ 18,014 Receivables — 245,950 40,797 (8,821 ) 277,926 Inventories — 189,536 31,146 (1,549 ) 219,133 Prepaid and other current assets 71 18,846 1,907 — 20,824 Total current assets 179 462,640 83,448 (10,370 ) 535,897 Property, plant and equipment, net — 222,425 13,642 — 236,067 Goodwill — 633,771 272,995 — 906,766 Advances due from affiliates 660,836 14,228 81,199 (756,263 ) — Intercompany notes receivable — 1,394 4 (1,398 ) — Investment in subsidiaries 978,944 688,890 542,462 (2,210,296 ) — Intangible assets, net — 207,694 89,703 — 297,397 Other assets and deferred charges 4,226 2,292 711 — 7,229 Total assets 1,644,185 2,233,334 1,084,164 (2,978,327 ) 1,983,356 Liabilities and Equity Accounts payable 30 113,497 22,397 (8,821 ) 127,103 Accrued compensation and employee benefits — 31,619 5,369 — 36,988 Other accrued expenses (3,811 ) 784,752 28,703 (756,590 ) 53,054 Total current liabilities (3,781 ) 929,868 56,469 (765,411 ) 217,145 Intercompany notes payable — 4 1,394 (1,398 ) — Long-term debt 683,206 4,321 16 — 687,543 Deferred income taxes — 73,089 20,049 — 93,138 Other long-term liabilities — 19,459 1,311 — 20,770 Total liabilities 679,425 1,026,741 79,239 (766,809 ) 1,018,596 Equity: Stockholders’ capital 964,760 1,213,290 1,034,542 (2,211,518 ) 1,001,074 Accumulated other comprehensive loss — (6,697 ) (31,830 ) — (38,527 ) Total stockholders’ equity 964,760 1,206,593 1,002,712 (2,211,518 ) 962,547 Noncontrolling interest — — 2,213 — 2,213 Total equity 964,760 1,206,593 1,004,925 (2,211,518 ) 964,760 Total liabilities and equity $ 1,644,185 $ 2,233,334 $ 1,084,164 $ (2,978,327 ) $ 1,983,356 December 31, 2017 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Assets Cash and cash equivalents $ — $ 5,763 $ 17,949 $ — $ 23,712 Receivables — 171,363 34,335 (3,674 ) 202,024 Inventories — 175,031 27,488 (928 ) 201,591 Prepaid and other current assets — 11,990 2,048 — 14,038 Total current assets — 364,147 81,820 (4,602 ) 441,365 Property, plant and equipment, net — 195,579 16,253 — 211,832 Goodwill — 633,734 276,354 — 910,088 Advances due from affiliates — 10,299 60,109 (70,408 ) — Investment in subsidiaries 1,640,034 801,235 388,315 (2,829,584 ) — Intangible assets, net — 234,795 103,715 — 338,510 Other assets and deferred charges — 2,129 851 — 2,980 Total assets 1,640,034 2,241,918 927,417 (2,904,594 ) 1,904,775 Liabilities and Equity Accounts payable — 83,864 18,636 (3,674 ) 98,826 Accrued compensation and employee benefits — 24,875 5,414 — 30,289 Other accrued expenses — 74,393 18,289 (70,732 ) 21,950 Total current liabilities — 183,132 42,339 (74,406 ) 151,065 Deferred income taxes — 75,075 21,910 — 96,985 Other liabilities — 16,657 34 — 16,691 Equity: Parent Company investment in Apergy 1,640,034 1,971,790 880,064 (2,830,188 ) 1,661,700 Accumulated other comprehensive loss — (4,736 ) (21,679 ) — (26,415 ) Total Parent Company equity 1,640,034 1,967,054 858,385 (2,830,188 ) 1,635,285 Noncontrolling interest — — 4,749 — 4,749 Total equity 1,640,034 1,967,054 863,134 (2,830,188 ) 1,640,034 Total liabilities and equity $ 1,640,034 $ 2,241,918 $ 927,417 $ (2,904,594 ) $ 1,904,775	December 31, 2017 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Assets Cash and cash equivalents $ — $ 5,763 $ 17,949 $ — $ 23,712 Receivables — 171,363 34,335 (3,674 ) 202,024 Inventories — 175,031 27,488 (928 ) 201,591 Prepaid and other current assets — 11,990 2,048 — 14,038 Total current assets — 364,147 81,820 (4,602 ) 441,365 Property, plant and equipment, net — 195,579 16,253 — 211,832 Goodwill — 633,734 276,354 — 910,088 Advances due from affiliates — 10,299 60,109 (70,408 ) — Investment in subsidiaries 1,640,034 801,235 388,315 (2,829,584 ) — Intangible assets, net — 234,795 103,715 — 338,510 Other assets and deferred charges — 2,129 851 — 2,980 Total assets 1,640,034 2,241,918 927,417 (2,904,594 ) 1,904,775 Liabilities and Equity Accounts payable — 83,864 18,636 (3,674 ) 98,826 Accrued compensation and employee benefits — 24,875 5,414 — 30,289 Other accrued expenses — 74,393 18,289 (70,732 ) 21,950 Total current liabilities — 183,132 42,339 (74,406 ) 151,065 Deferred income taxes — 75,075 21,910 — 96,985 Other liabilities — 16,657 34 — 16,691 Equity: Parent Company investment in Apergy 1,640,034 1,971,790 880,064 (2,830,188 ) 1,661,700 Accumulated other comprehensive loss — (4,736 ) (21,679 ) — (26,415 ) Total Parent Company equity 1,640,034 1,967,054 858,385 (2,830,188 ) 1,635,285 Noncontrolling interest — — 4,749 — 4,749 Total equity 1,640,034 1,967,054 863,134 (2,830,188 ) 1,640,034 Total liabilities and equity $ 1,640,034 $ 2,241,918 $ 927,417 $ (2,904,594 ) $ 1,904,775 December 31, 2016 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Assets Cash and cash equivalents $ — $ 3,730 $ 22,297 $ — $ 26,027 Receivables — 116,340 29,511 (6,366 ) 139,485 Inventories — 161,314 23,979 (735 ) 184,558 Prepaid and other current assets — 4,090 2,161 — 6,251 Total current assets — 285,474 77,948 (7,101 ) 356,321 Property, plant and equipment, net — 180,292 21,455 — 201,747 Goodwill — 633,734 268,845 — 902,579 Advances due from affiliates — 10,464 64,521 (74,985 ) — Investment in subsidiaries 1,551,353 753,916 348,046 (2,653,315 ) — Intangible assets, net — 273,127 113,690 — 386,817 Other assets and deferred charges — 2,499 932 — 3,431 Total assets 1,551,353 2,139,506 895,437 (2,735,401 ) 1,850,895 Liabilities and Equity Accounts payable — 53,195 19,451 (6,366 ) 66,280 Accrued compensation and employee benefits — 20,450 4,338 — 24,788 Other accrued expenses — 81,402 15,466 (75,242 ) 21,626 Total current liabilities — 155,047 39,255 (81,608 ) 112,694 Deferred income taxes — 125,490 42,075 — 167,565 Other liabilities — 19,009 274 — 19,283 Equity: Parent Company investment in Apergy 1,551,353 1,847,548 834,843 (2,653,793 ) 1,579,951 Accumulated other comprehensive loss — (7,588 ) (26,041 ) — (33,629 ) Total Parent Company equity 1,551,353 1,839,960 808,802 (2,653,793 ) 1,546,322 Noncontrolling interest — — 5,031 — 5,031 Total equity 1,551,353 1,839,960 813,833 (2,653,793 ) 1,551,353 Total liabilities and equity $ 1,551,353 $ 2,139,506 $ 895,437 $ (2,735,401 ) $ 1,850,895
Schedule of Condensed Statements of Income	Three Months Ended September 30, 2018 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Product revenue $ — $ 250,549 $ 32,553 $ — $ 283,102 Service revenue — 13,757 6,714 — 20,471 Lease and other revenue — 12,531 364 — 12,895 Related party revenue — 5,944 4,853 (10,797 ) — Total revenue — 282,781 44,484 (10,797 ) 316,468 Cost of goods and services — 175,718 37,899 (10,883 ) 202,734 Gross profit — 107,063 6,585 86 113,734 Selling, general and administrative expense 87 63,470 5,465 — 69,022 Interest expense, net 10,491 84 9 — 10,584 Other expense (income), net — (524 ) 1,434 — 910 Income (loss) before income taxes and equity in earnings of affiliates (10,578 ) 44,033 (323 ) 86 33,218 Provision for (benefit from) income taxes (2,575 ) 8,744 1,536 18 7,723 Income (loss) before equity in earnings of affiliates (8,003 ) 35,289 (1,859 ) 68 25,495 Equity in earnings of affiliates 33,266 5,344 12,604 (51,214 ) — Net income 25,263 40,633 10,745 (51,146 ) 25,495 Net income attributable to noncontrolling interest — — 232 — 232 Net income attributable to Apergy $ 25,263 $ 40,633 $ 10,513 $ (51,146 ) $ 25,263 Comprehensive income attributable to Apergy $ 25,187 $ 39,904 $ 11,166 $ (51,070 ) $ 25,187 Three Months Ended September 30, 2017 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Product revenue $ — $ 203,623 $ 32,225 $ — $ 235,848 Service revenue — 9,419 6,729 — 16,148 Lease and other revenue — 6,296 351 — 6,647 Related party revenue — 7,656 3,232 (10,877 ) 11 Total revenue — 226,994 42,537 (10,877 ) 258,654 Cost of goods and services — 148,389 36,261 (10,770 ) 173,880 Gross profit — 78,605 6,276 (107 ) 84,774 Selling, general and administrative expense — 50,448 4,380 — 54,828 Interest expense, net — 78 1 — 79 Other expense, net — 2,816 124 1 2,941 Income before income taxes and equity in earnings of affiliates — 25,263 1,771 (108 ) 26,926 Provision for income taxes — 7,938 340 (37 ) 8,241 Income before equity in earnings of affiliates — 17,325 1,431 (71 ) 18,685 Equity in earnings of affiliates 18,421 2,435 3,006 (23,862 ) — Net income 18,421 19,760 4,437 (23,933 ) 18,685 Net income attributable to noncontrolling interest — — 264 — 264 Net income attributable to Apergy $ 18,421 $ 19,760 $ 4,173 $ (23,933 ) $ 18,421 Comprehensive income attributable to Apergy $ 23,791 $ 20,195 $ 9,108 $ (29,303 ) $ 23,791 Nine Months Ended September 30, 2018 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Product revenue $ — $ 714,226 $ 94,084 $ — $ 808,310 Service revenue — 42,344 19,670 — 62,014 Lease and other revenue — 34,855 1,139 — 35,994 Related party revenue — 18,598 13,565 (32,163 ) — Total revenue — 810,023 128,458 (32,163 ) 906,318 Cost of goods and services — 515,005 111,142 (31,542 ) 594,605 Gross profit — 295,018 17,316 (621 ) 311,713 Selling, general and administrative expense 1,588 176,733 16,247 — 194,568 Interest expense, net 16,494 288 32 (1 ) 16,813 Other expense, net — 1,872 1,851 1 3,724 Income (loss) before income taxes and equity in earnings of affiliates (18,082 ) 116,125 (814 ) (621 ) 96,608 Provision for (benefit from) income taxes (4,217 ) 24,076 4,595 (130 ) 24,324 Income (loss) before equity in earnings of affiliates (13,865 ) 92,049 (5,409 ) (491 ) 72,284 Equity in earnings of affiliates 85,854 18,811 37,568 (142,233 ) — Net income 71,989 110,860 32,159 (142,724 ) 72,284 Net income attributable to noncontrolling interest — — 295 — 295 Net income attributable to Apergy $ 71,989 $ 110,860 $ 31,864 $ (142,724 ) $ 71,989 Comprehensive income attributable to Apergy $ 63,613 $ 110,214 $ 24,134 $ (134,348 ) $ 63,613 Nine Months Ended September 30, 2017 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Product revenue $ — $ 590,554 $ 89,283 $ — $ 679,837 Service revenue — 25,060 21,103 — 46,163 Lease and other revenue — 17,501 1,573 — 19,074 Related party revenue — 19,477 9,702 (29,160 ) 19 Total revenue — 652,592 121,661 (29,160 ) 745,093 Cost of goods and services — 425,792 103,259 (28,722 ) 500,329 Gross profit — 226,800 18,402 (438 ) 244,764 Selling, general and administrative expense — 149,145 13,214 — 162,359 Interest expense, net — 196 3 — 199 Other expense, net — 7,611 318 — 7,929 Income before income taxes and equity in earnings of affiliates — 69,848 4,867 (438 ) 74,277 Provision for income taxes — 22,726 400 (153 ) 22,973 Income before equity in earnings of affiliates — 47,122 4,467 (285 ) 51,304 Equity in earnings of affiliates 50,444 5,579 5,446 (61,469 ) — Net income 50,444 52,701 9,913 (61,754 ) 51,304 Net income attributable to noncontrolling interest — — 860 — 860 Net income attributable to Apergy $ 50,444 $ 52,701 $ 9,053 $ (61,754) $ 50,444 Comprehensive income attributable to Apergy $ 57,538 $ 53,055 $ 15,793 $ (68,848) $ 57,538	Year Ended December 31, 2017 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments Total Revenue $ — $ 881,187 $ 164,507 $ (36,103 ) $ 1,009,591 Cost of goods and services — 586,519 140,516 (35,911 ) 691,124 Gross profit — 294,668 23,991 (192 ) 318,467 Selling, general and administrative expense — 200,839 18,678 — 219,517 Operating income (loss) — 93,829 5,313 (192 ) 98,950 Other expense, net — 9,429 237 — 9,666 Income before income taxes and equity in earnings of affiliates — 84,400 5,076 (192 ) 89,284 Benefit from income taxes — (10,680 ) (11,537 ) (67 ) (22,284 ) Income before equity in earnings of affiliates — 95,080 16,613 (125 ) 111,568 Equity in earnings of affiliates 110,638 22,110 11,020 (143,768 ) — Net income 110,638 117,190 27,633 (143,893 ) 111,568 Net income attributable to noncontrolling interest — — 930 — 930 Net income attributable to Apergy $ 110,638 $ 117,190 $ 26,703 $ (143,893 ) $ 110,638 Comprehensive income attributable to Apergy $ 117,852 $ 120,042 $ 31,065 $ (151,102 ) $ 117,852 Year Ended December 31, 2016 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments Total Revenue $ — $ 644,392 $ 142,614 $ (35,669 ) $ 751,337 Cost of goods and services — 459,465 132,350 (35,806 ) 556,009 Gross profit — 184,927 10,264 137 195,328 Selling, general and administrative expense — 183,892 21,517 — 205,409 Operating income (loss) — 1,035 (11,253 ) 137 (10,081 ) Other expense, net — 8,550 203 0 8,753 Loss before income taxes and equity in earnings of affiliates — (7,515 ) (11,456 ) 137 (18,834 ) Benefit from income taxes — (2,750 ) (5,341 ) 48 (8,043 ) Loss before equity in losses of affiliates — (4,765 ) (6,115 ) 89 (10,791 ) Equity in losses of affiliates (12,642 ) (23,668 ) (8,273 ) 44,583 — Net loss (12,642 ) (28,433 ) (14,388 ) 44,672 (10,791 ) Net income attributable to noncontrolling interest — — 1,851 — 1,851 Net loss attributable to Apergy $ (12,642 ) $ (28,433 ) $ (16,239 ) $ 44,672 $ (12,642 ) Comprehensive loss attributable to Apergy $ (11,577 ) $ (28,402 ) $ (15,205 ) $ 43,607 $ (11,577 ) Year Ended December 31, 2015 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments Total Revenue $ — $ 923,957 $ 192,682 $ (39,959 ) $ 1,076,680 Cost of goods and services — 604,715 177,504 (40,178 ) 742,041 Gross profit — 319,242 15,178 219 334,639 Selling, general and administrative expense — 220,897 24,826 — 245,723 Operating income (loss) — 98,345 (9,648 ) 219 88,916 Other expense (income), net — 10,606 (376 ) 1421 11,651 Income (loss) before income taxes and equity in earnings (losses) of affiliates — 87,739 (9,272 ) (1,202 ) 77,265 Provision for (benefit from) income taxes — 29,485 (5,431 ) 77 24,131 Income (loss) before equity in earnings of affiliates — 58,254 (3,841 ) (1,279 ) 53,134 Equity in earnings (losses) of affiliates 51,698 (17,980 ) 2,762 (36,480 ) — Net income (loss) 51,698 40,274 (1,079 ) (37,759 ) 53,134 Net income attributable to noncontrolling interest — — 1,436 — 1,436 Net income (loss) attributable to Apergy $ 51,698 $ 40,274 $ (2,515 ) $ (37,759 ) $ 51,698 Comprehensive income (loss) attributable to Apergy $ 39,738 $ 39,594 $ (13,795 ) $ (25,799 ) $ 39,738
Schedule of Condensed Statements of Cash Flows	Nine Months Ended September 30, 2018 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Cash provided (required) by operating activities $ (16,694 ) $ 103,911 $ 6,588 $ (999 ) $ 92,806 Cash provided (required) by investing activities: Capital expenditures — (43,746 ) (2,086 ) — (45,832 ) Proceeds from sale of property, plant, and equipment — 938 32 — 970 Purchase price adjustments on acquisition — — 53 — 53 Net cash required by investing activities — (42,808 ) (2,001 ) — (44,809 ) Cash provided (required) by financing activities: Proceeds from long-term debt, net of discounts 713,963 — — — 713,963 Payment of debt issue costs (16,006 ) — — — (16,006 ) Repayment of long-term debt (20,000 ) — — — (20,000 ) Advances due to/(from) affiliates (660,836 ) 677,999 (17,163 ) — — Net transfers to Parent Company and intercompany distributions (319 ) (736,557 ) 7,020 999 (728,857 ) Distributions to noncontrolling interest — — (2,720 ) — (2,720 ) Net cash provided (required) by financing activities 16,802 (58,558 ) (12,863 ) 999 (53,620 ) Effect of exchange rate changes on cash and cash equivalents — — (75 ) — (75 ) Net increase (decrease) in cash and cash equivalents 108 2,545 (8,351 ) — (5,698 ) Cash and cash equivalents at beginning of period — 5,763 17,949 — 23,712 Cash and cash equivalents at end of period $ 108 $ 8,308 $ 9,598 $ — $ 18,014 Nine Months Ended September 30, 2017 (in thousands) Apergy Subsidiary Subsidiary non-guarantors Adjustments and Total Cash provided by operating activities $ — $ 38,153 $ 2,899 $ 153 $ 41,205 Cash provided (required) by investing activities: Capital expenditures — (28,221 ) (1,224 ) — (29,445 ) Proceeds from sale of property, plant, and equipment — 2,596 20 — 2,616 Net cash required by investing activities — (25,625 ) (1,204 ) — (26,829 ) Cash provided (required) by financing activities: Net transfers to Parent Company and intercompany distributions — (13,132 ) (5,935 ) (153 ) (19,220 ) Distributions to noncontrolling interest — — (1,212 ) — (1,212 ) Net cash required by financing activities — (13,132 ) (7,147 ) (153 ) (20,432 ) Effect of exchange rate changes on cash and cash equivalents — — 3,476 — 3,476 Net decrease in cash and cash equivalents — (604 ) (1,976 ) — (2,580 ) Cash and cash equivalents at beginning of period — 3,730 22,297 — 26,027 Cash and cash equivalents at end of period $ — $ 3,126 $ 20,321 $ — $ 23,447	Year Ended December 31, 2017 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Cash provided (required) by operating activities $ — $ 65,289 $ 11,561 $ 67 $ 76,917 Cash provided (required) by investing activities: Additions to property, plant and equipment — (39,565 ) (1,646 ) — (41,211 ) Proceeds from sale of property, plant, and equipment — 3,433 114 — 3,547 Acquisition (net of cash and cash equivalents acquired) — — (8,842 ) — (8,842 ) Net cash required by investing activities — (36,132 ) (10,374 ) — (46,506 ) Cash provided (required) by financing activities: Change in borrowings, net — — (599 ) — (599 ) Distributions to noncontrolling interest — — (1,212 ) — (1,212 ) Net transfers to Parent Company and intercompany distributions — (27,124 ) (4,001 ) (67 ) (31,192 ) Net cash required by financing activities — (27,124 ) (5,812 ) (67 ) (33,003 ) Effect of exchange rate changes on cash and cash equivalents — — 277 — 277 Net increase (decrease) in cash and cash equivalents — 2,033 (4,348 ) — (2,315 ) Cash and cash equivalents at beginning of period — 3,730 22,297 — 26,027 Cash and cash equivalents at end of period $ — $ 5,763 $ 17,949 $ — $ 23,712 Year Ended December 31, 2016 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Cash provided by operating activities $ — $ 103,788 $ 25,979 $ (48 ) $ 129,709 Cash provided (required) by investing activities: Additions to property, plant and equipment — (23,080 ) (3,774 ) — (26,854 ) Proceeds from sale of property, plant, and equipment — 2,245 281 — 2,526 Additions to intangible assets — (3,700 ) — — (3,700 ) Net cash required by investing activities — (24,535 ) (3,493 ) — (28,028 ) Cash provided (required) by financing activities: Distributions to noncontrolling interest — — (1,727 ) — (1,727 ) Net transfers to Parent Company and intercompany distributions — (78,232 ) (6,070 ) 48 (84,254 ) Net cash required by financing activities — (78,232 ) (7,797 ) 48 (85,981 ) Effect of exchange rate changes on cash and cash equivalents — — (90 ) — (90 ) Net increase in cash and cash equivalents — 1,011 14,599 — 15,610 Cash and cash equivalents at beginning of period — 2,719 7,698 — 10,417 Cash and cash equivalents at end of period $ — $ 3,730 $ 22,297 $ — $ 26,027 Year Ended December 31, 2015 (in thousands) Apergy Subsidiary Subsidiary non- Adjustments Total Cash provided (required) by operating activities $ — $ 137,352 $ 79,817 $ (1,498 ) $ 215,671 Cash provided (required) by investing activities: Additions to property, plant and equipment — (30,750 ) (1,235 ) — (31,985 ) Proceeds from sale of property, plant, and equipment — 3,814 4,070 — 7,884 Additions to intangible assets — (10,000 ) — — (10,000 ) Net cash provided (required) by investing activities — (36,936 ) 2,835 — (34,101 ) Cash provided (required) by financing activities: Net transfers to Parent Company and intercompany distributions — (108,909 ) (87,566 ) 1,498 (194,977 ) Net cash provided by (required by) financing activities — (108,909 ) (87,566 ) 1,498 (194,977 ) Effect of exchange rate changes on cash and cash equivalents — — (531 ) — (531 ) Net decrease in cash and cash equivalents — (8,493 ) (5,445 ) — (13,938 ) Cash and cash equivalents at beginning of period — 11,212 13,143 — 24,355 Cash and cash equivalents at end of period $ — $ 2,719 $ 7,698 $ — $ 10,417

Other Accrued Expenses and Ot_2

Other Accrued Expenses and Other Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Schedule of the Major Components of Other Accrued Expenses (Current)	The following table details the major components of Other accrued expenses (current): December 31, December 31, Unearned/deferred revenue $ 4,487 $ 3,787 Warranty 2,978 4,568 Restructuring and exit costs 2,551 459 Taxes other than income 2,432 1,424 Accrued freight, travel and transportation 1,397 1,384 Short-term capital lease obligations 1,041 694 Accrued rebates 617 473 Other (none of which are individually significant) 6,447 8,837 Total other accrued expenses $ 21,950 $ 21,626
Schedule of the Major Components Of Other Liabilities (Noncurrent)	The following table details the major components of Other liabilities (noncurrent): December 31, December 31, Defined benefit and other post-retirement benefit plans $ 12,650 $ 16,510 Long-term capital lease obligations 3,742 1,919 Warranty 92 98 Other (none of which are individually significant) 207 756 Total other liabilities $ 16,691 $ 19,283
Schedule of the Changes in the Carrying Amount of Product Warranties	The changes in the carrying amount of product warranties were as follows: Years Ended December 31, 2017 2016 2015 Balance, beginning of year $ 4,666 $ 4,421 $ 6,717 Provision for warranties 309 2,109 1,266 Settlements made (1,896 ) (1,518 ) (3,168 ) Other adjustments, including currency translation (9 ) (346 ) (394 ) Balance, end of year $ 3,070 $ 4,666 $ 4,421

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	Income taxes have been based on the following components of income (loss) before income taxes in the Combined Statements of Income: Years Ended December 31, 2017 2016 2015 Domestic $ 66,852 $ (25,926 ) $ 61,670 Foreign 22,432 7,092 15,595 Total $ 89,284 $ (18,834 ) $ 77,265
Schedule of Components of Income Tax Expense (Benefit)	Income tax (benefit) expense relating to continuing operations for the years ended December 31, 2017 and 2016 is comprised of the following: Years Ended December 31, 2017 2016 2015 Current: U.S. federal $ 42,312 $ 8,872 $ 40,415 State and local 4,230 1,995 (332 ) Foreign 6,176 971 5,344 Total current 52,718 11,838 45,427 Deferred: U.S. federal (73,544 ) (19,161 ) (23,135 ) State and local (1,361 ) (771 ) 4,141 Foreign (97 ) 51 (2,302 ) Total deferred (75,002 ) (19,881 ) (21,296 ) Total (benefit) expense $ (22,284 ) $ (8,043 ) $ 24,131
Schedule of Effective Income Tax Rate Reconciliation	Differences between the effective income tax rate and the U.S. federal income statutory tax rate are as follows: Years Ended 2017 2016 2015 U.S. federal income tax rate 35.0 % 35.0 % 35.0 % State and local taxes, net of federal income tax benefit 2.1 (3.9 ) 3.1 Foreign operations tax effect (2.8 ) 7.8 (3.1 ) Research and experimentation tax credits (0.7 ) 2.3 (0.7 ) Domestic manufacturing deduction (4.5 ) 6.2 (4.6 ) Nondeductible expenses 0.7 (3.3 ) 1.0 ESOP dividends (0.2 ) 2.9 (0.7 ) Branch income 1.1 (2.9 ) 0.8 Changes due to the Tax Reform Act (55.2 ) — — Other (0.5 ) (1.4 ) 0.4 Effective tax rate from continuing operations (25.0 )% 42.7 % 31.2 %
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences that give rise to future deferred tax assets and liabilities are as follows: December 31, December 31, Deferred Tax Assets: Accrued compensation, principally post-retirement and other employee benefits $ 4,568 $ 9,126 Accrued expenses, principally for state income taxes, interest and warranty 846 1,512 Net operating loss and other carryforwards 1,280 1,082 Accounts receivable, principally due to allowance for doubtful accounts 827 1,780 Long-term liabilities, principally warranty, environmental and exit cost 678 620 Other assets 132 459 Total gross deferred tax assets 8,331 14,579 Valuation allowance (1,280 ) (1,082 ) Total deferred tax assets, net of valuation allowances $ 7,051 $ 13,497 Deferred Tax Liabilities: Inventories, principally due to reserves for financial reporting purposes and capitalization for tax purposes $ (3,687 ) $ (4,754 ) Intangible assets, principally due to different tax and financial reporting bases and amortization lives (83,669 ) (149,500 ) Property, plant and equipment, principally due to differences in depreciation (16,134 ) (26,254 ) Total gross deferred tax liabilities (103,490 ) (180,508 ) Net deferred tax liability $ (96,439 ) $ (167,011 ) Classified as follows in the Combined Balance Sheets: Other assets and deferred charges $ 546 $ 554 Deferred income taxes (96,985 ) (167,565 ) $ (96,439 ) $ (167,011 )

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments for Operating and Capital Leases	The aggregate future minimum lease payments for operating and capital leases as of December 31, 2017 are as follows: Operating Capital 2018 $ 11,668 $ 2,232 2019 10,646 1,696 2020 7,639 181 2021 5,309 — 2022 4,625 — Thereafter 5,105 — Total $ 44,992 $ 4,109

Employee Benefit Plans and No_2

Employee Benefit Plans and Non-Qualified Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Summary of Expenses Recorded in the Financial Statements	The table below summarizes the expenses recorded in the Apergy financial statements for the Dover plans in which Apergy participates. Years Ended December 31, 2017 2016 2015 Plan Name Dover U.S. Pension Plan $ 3,922 $ 4,643 $ 4,783 Canada Salaried Pension Plan 554 1,615 513 Other non-qualified 108 121 123
Summary of Combined Balance Sheets Impact Associated with the Company's Single Employer Defined Benefit Plans	The following tables summarize the Combined Balance Sheets impact, including the benefit obligations, assets and funded status associated with the Company’s single employer defined benefit plans at December 31, 2017 and 2016. Non-U.S. Qualified Defined Non-Qualified 2017 2016 2017 2016 Change in benefit obligation: Benefit obligation at beginning of year $ 3,512 $ 3,139 $ 18,600 $ 20,313 Service cost 106 102 — — Interest cost 137 129 621 719 Benefits paid (99 ) (79 ) (1,710 ) (2,484 ) Actuarial loss (gain) (22 ) 170 (3,314 ) 52 Currency translation and other 247 51 — — Benefit obligation at end of year 3,881 3,512 14,197 18,600 Change in plan assets: Fair value of plan assets at beginning of year 3,391 3,056 — — Actual return on plan assets 290 198 — — Company contributions 166 165 1,710 2,484 Benefits paid (99 ) (79 ) (1,710 ) (2,484 ) Currency translation and other 245 51 — — Fair value of plan assets at end of year 3,993 3,391 — — Funded (unfunded) status $ 112 $ (121 ) $ (14,197 ) $ (18,600 ) Amounts recognized in the Combined Balance Sheets consist of: Assets and Liabilities: Other assets and deferred charges $ 112 $ — $ — $ — Accrued compensation and employee benefits — — (1,547 ) (2,211 ) Other liabilities — (121 ) (12,650 ) (16,389 ) Total assets and liabilities 112 (121 ) (14,197 ) (18,600 ) Accumulated Other Comprehensive Loss (Income): Net actuarial losses 1,449 1,632 6,078 9,721 Prior service cost 40 42 — — Net asset at transition, other (20 ) (21 ) — — Deferred taxes (397 ) (446 ) (2,670 ) (3,592 ) Total accumulated other comprehensive loss, net of tax 1,072 1,207 3,408 6,129 Net amount recognized at December 31, $ 1,184 $ 1,086 $ (10,789 ) $ (12,471 ) Accumulated benefit obligations $ 3,881 $ 3,512 $ 14,197 $ 18,600
Summary of Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets	Pension plans with accumulated benefit obligations in excess of plan assets consist of the following at December 31, 2017 and 2016: 2017 2016 Projected benefit obligation (PBO) $ — $ 3,512 Accumulated benefit obligation (ABO) — 3,512 Fair value of plan assets — 3,391
Components of the Net Periodic Benefit Cost	Components of the net periodic benefit cost were as follows: Defined Benefit Plans Non-U.S. Qualified Defined Benefit Plan Non-Qualified 2017 2016 2015 2017 2016 2015 Service cost $ 106 $ 102 $ 118 $ — $ — $ — Interest cost 137 129 130 621 719 708 Expected return on plan assets (198 ) (186 ) (184 ) — — — Amortization of: Prior service cost 2 2 2 — — — Recognized actuarial loss 68 58 57 330 305 284 Transition obligation (1 ) (1 ) (1 ) — — — Other — — — (1 ) — — Total net periodic benefit cost $ 114 $ 104 $ 122 $ 950 $ 1,024 $ 992
Schedule of Amounts Expected to be Amortized from Accumulated Other Comprehensive Income (loss) into Net Periodic Benefit Cost	Amounts expected to be amortized from Accumulated other comprehensive income (loss) into net periodic benefit cost during 2018 are as follows: Non-U.S. Non-Qualified Amortization of: Prior service cost $ 2 $ — Recognized actuarial loss 55 205 Transition obligation (1 ) — Total $ 56 $ 205
Weighted Average Assumptions Used in Determining the Benefit Obligations	The Company determines actuarial assumptions on an annual basis. The weighted average assumptions used in determining the benefit obligations were as follows: Non-U.S. Non-Qualified 2017 2016 2017 2016 Discount rate 3.50 % 3.75 % 3.35 % 3.55 %
Weighted Average Assumptions Used in Determining the Net Periodic Benefit Cost	The weighted average assumptions used in determining the net periodic benefit cost were as follows: Non-U.S. Non-Qualified 2017 2016 2017 2016 Discount rate 3.75 % 4.00 % 3.55 % 3.75 % Expected return on plan assets 5.50 % 5.75 % na na
Actual and Target Weighted Average Asset Allocation	The Company’s actual and target weighted average asset allocation for our non-U.S. 2017 2016 Current Equity securities 61 % 60 % 60 % Fixed income 38 % 39 % 40 % Real estate and other 1 % 1 % — % Total 100 % 100 % 100 %
Fair Values of Pension Plan Assets by Asset Category within the Fair Value Hierarchy	The fair values of the non-U.S. Non-U.S. December 31, 2017 December 31, 2016 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Mutual funds $ 2,399 $ 1,594 $ — $ 3,993 $ 2,104 $ 1,287 $ — $ 3,391 Total $ 2,399 $ 1,594 $ — $ 3,993 $ 2,104 $ 1,287 $ — $ 3,391 * A revision was made to the fair value leveling hierarchy in the above table as of December 31, 2016. The change was from level 2 to 1. The valuation techniques were unchanged and the amounts revised were not material to the prior annual period.
Estimated Future Benefit Payments to Retirees	Estimated future benefit payments to retirees, which reflect expected future service, are as follows: Non-U.S. Non-Qualified 2018 $ 86 $ 1,572 2019 94 1,472 2020 92 1,368 2021 100 1,261 2022 107 1,154 2023 - 2027 709 4,163

Quarterly Information (Unaudi_2

Quarterly Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information (Unaudited)	2017 2016 (in thousands, except per share data) 4th Qtr. 3rd Qtr. 2nd Qtr. 1st Qtr. 4th Qtr. 3rd Qtr. 2nd Qtr. 1st Qtr. Revenue $ 264,498 $ 258,654 $ 256,161 $ 230,278 $ 201,176 $ 185,455 $ 168,535 $ 196,171 Gross profit 73,703 84,774 84,630 75,360 61,012 47,254 32,610 54,452 Net income (loss) 60,264 18,685 19,033 13,586 4,167 (2,154 ) (10,294 ) (2,510 ) Net income (loss) attributable to Apergy 60,194 18,421 18,754 13,269 3,769 (2,503 ) (10,872 ) (3,036 ) Basic earnings per share (1) $ 0.78 $ 0.24 $ 0.24 $ 0.17 $ 0.05 $ (0.03 ) $ (0.14 ) $ (0.04 ) Diluted earnings per share (1) $ 0.77 $ 0.24 $ 0.24 $ 0.17 $ 0.05 $ (0.03 ) $ (0.14 ) $ (0.04 ) (1) On May 9, 2018, 77,339,828 shares of our common stock were distributed to Dover stockholders in conjunction with the Separation. For comparative purposes, we have assumed the shares issued in conjunction with the Separation to be outstanding as of the beginning of each period prior to the Separation. In addition, we have assumed the potential dilutive securities outstanding as of May 8, 2018, were outstanding and fully dilutive in each of the periods prior to the Separation.

Basis of Presentation and Sep_3

Basis of Presentation and Separation Separation and Distribution (Detail)	May 09, 2018USD ($)shares	May 03, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
Number of companies separated	2
Common stock issued (in shares) | shares	77,339,828
Conversion ratio	0.5
Tax matters agreement, minimum percentage change in stock ownership	40.00%
Principal amount of debt issued	$ 715,000,000
Business separation payment	700,000,000	$ 700,000,000
Intercompany notes payable			$ 224,500,000	$ 233,100,000
Term Loan Facility
Debt Instrument [Line Items]
Principal amount of debt issued	$ 415,000,000
6.375% Senior Notes Due May 2026 | Senior Notes
Debt Instrument [Line Items]
Principal amount of debt issued		$ 300,000,000

Basis of Presentation and Sep_4

Basis of Presentation and Separation Basis of Presentation (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2017
Selling, General and Administrative Expenses [Member]
Basis Of Presentation And Organization [Line Items]
Prior Period Reclassification Adjustment		$ 11	$ 32.1
Other Noncurrent Liabilities [Member]
Basis Of Presentation And Organization [Line Items]
Prior Period Reclassification Adjustment	$ 3.7

New Accounting Standards New Ac

New Accounting Standards New Accounting Standards (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting changes	$ 1,300
Accounting Standards Update 2016-15
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting changes	9,600	$ 14,500	$ 1,100	$ 7,800
Net Parent Investment in Apergy
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting changes	$ 1,315

Related Party Transactions (Det

Related Party Transactions (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related party transaction, selling, general and administrative expenses from transactions with related party	$ 4,700	$ 7,400	$ 16,500	$ 22,987	$ 19,459	$ 20,852
Payments of ordinary dividends, noncontrolling interest		$ 2,720	1,212	$ 1,212	1,727
Non-controlling Interest
Related party transaction, commission rate		5.00%		5.00%
Royalty Agreements [Member]
Related party transaction, expenses from transactions with related party	$ 2,500	$ 2,300	$ 7,400	$ 9,800	7,400	10,400
Patents and Copyrights [Member]
Related party transaction, expenses from transactions with related party					$ 3,700	$ 10,000

Earnings per Share (Detail)

Earnings per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	May 09, 2018	Sep. 30, 2018	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Common stock issued (in shares)	77,339,828
Net income attributable to Apergy		$ 25,263	$ 60,194		$ 18,421		$ 18,754		$ 13,269		$ 3,769		$ (2,503)		$ (10,872)		$ (3,036)		$ 71,989	$ 50,444	$ 110,638	$ (12,642)	$ 51,698
Weighted-average number of shares outstanding		77,340,000			77,340,000														77,340,000	77,340,000
Dilutive effect of stock-based compensation		229,000			550,000														402,000	550,000
Total shares and dilutive securities		77,569,000			77,890,000														77,742,000	77,890,000
Basic earnings per share attributable to Apergy (in dollars per share)		$ 0.33	$ 0.78	[1]	$ 0.24	[1]	$ 0.24	[1]	$ 0.17	[1]	$ 0.05	[1]	$ (0.03)	[1]	$ (0.14)	[1]	$ (0.04)	[1]	$ 0.93	$ 0.65
Diluted earnings per share attributable to Apergy (in dollars per share)		$ 0.33	$ 0.77	[1]	$ 0.24	[1]	$ 0.24	[1]	$ 0.17	[1]	$ 0.05	[1]	$ (0.03)	[1]	$ (0.14)	[1]	$ (0.04)	[1]	$ 0.93	$ 0.65
[1]	On May 9, 2018, 77,339,828 shares of our common stock were distributed to Dover stockholders in conjunction with the Separation. For comparative purposes, we have assumed the shares issued in conjunction with the Separation to be outstanding as of the beginning of each period prior to the Separation. In addition, we have assumed the potential dilutive securities outstanding as of May 8, 2018, were outstanding and fully dilutive in each of the periods prior to the Separation.

Inventories (Detail)

Inventories (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Inventory, Net [Abstract]
Raw materials	$ 48,735	$ 45,408	$ 45,209
Work in progress	11,130	10,879	10,321
Finished goods	184,871	167,416	153,040
Subtotal	244,736	223,703	208,570
LIFO and valuation adjustments	(25,603)	(22,112)	(24,012)
Inventories, net	$ 219,133	$ 201,591	$ 184,558

Property, Plant and Equipment_2

Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Cost	$ 618,797		$ 559,051	$ 503,068
Accumulated depreciation	(382,730)		(347,219)	(301,321)
Property, plant and equipment, net	236,067		211,832	201,747
Transfers from inventory	42,500
Depreciation expense	52,814	$ 42,233	58,178	56,068	$ 60,831
Land [Member]
Property, Plant and Equipment [Line Items]
Cost	13,623		13,557	14,636
Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Cost	104,026		99,233	91,927
Machinery, equipment and other [Member]
Property, Plant and Equipment [Line Items]
Cost	$ 501,148		$ 446,261	$ 396,505

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Goodwill (Detail) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Balance		$ 910,088	$ 902,579	$ 901,928
Acquisitions			5,053
Purchase price adjustment	[1]	(53)
Foreign currency translation		(3,269)	2,456	651
Balance		906,766	910,088	902,579
Production and Automation Technologies [Member]
Goodwill [Roll Forward]
Balance		808,952	801,443	800,792
Acquisitions			5,053
Purchase price adjustment	[1]	(53)
Foreign currency translation		(3,269)	2,456	651
Balance		805,630	808,952	801,443
Drilling Technologies [Member]
Goodwill [Roll Forward]
Balance		101,136	101,136	101,136
Purchase price adjustment	[1]	0
Foreign currency translation		0		0
Balance		$ 101,136	$ 101,136	$ 101,136
[1]	Purchase price adjustment related to our 2017 acquisition of PCP Oil Tools S.A. and Ener Tools S.A.

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Intangible Assets and Amortization Expense (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 662,746	$ 665,555	$ 658,975
Accumulated amortization	368,949	330,645	275,758
Finite-Lived Intangible Assets, Net	293,797	334,910	383,217
Intangible Assets, Gross (Excluding Goodwill)	666,346	669,155	662,575
Intangible assets, net	297,397	338,510	386,817
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	0	0	0
Indefinite-Lived Intangible Assets (Excluding Goodwill)	3,600	3,600	3,600
Customer Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	569,832	572,415	566,602
Accumulated amortization	309,355	276,655	229,902
Finite-Lived Intangible Assets, Net	260,477	295,760	336,700
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	36,307	36,312	36,296
Accumulated amortization	20,648	17,821	14,013
Finite-Lived Intangible Assets, Net	15,659	18,491	22,283
Patents [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	38,514	38,679	38,106
Accumulated amortization	22,959	20,449	16,662
Finite-Lived Intangible Assets, Net	15,555	18,230	21,444
Unpatented Technologies [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	9,700	9,700	9,700
Accumulated amortization	9,700	9,700	9,700
Drawings and Manuals [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	3,047	3,067	3,001
Accumulated amortization	2,163	2,109	1,942
Finite-Lived Intangible Assets, Net	884	958	1,059
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,346	5,382	5,270
Accumulated amortization	4,124	3,911	3,539
Finite-Lived Intangible Assets, Net	$ 1,222	$ 1,471	$ 1,731

Debt - Long-term Debt (Detail)

Debt - Long-term Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Capital leases	$ 4,337	$ 3,742
Total	699,337	3,742
Net unamortized discounts and issuance costs	(11,794)	0
Total long-term debt	687,543	3,742
Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	0	0
Term Loan Facility
Debt Instrument [Line Items]
Long-term debt, gross	395,000	0
Senior Notes | 6.375% Senior Notes Due May 2026
Debt Instrument [Line Items]
Long-term debt, gross	$ 300,000	$ 0

Debt (Detail)

Debt (Detail)	May 09, 2018USD ($)	May 03, 2018USD ($)	Sep. 30, 2018USD ($)
Debt Instrument [Line Items]
Principal amount of debt issued	$ 715,000,000
Proceeds from long-term debt, net of discounts			$ 713,963,000
Cash payment to Dover	(700,000,000)	$ (700,000,000)
Registration right agreement term, point before annual interest rate increase		1 year
Senior Notes | 6.375% Senior Notes Due May 2026
Debt Instrument [Line Items]
Principal amount of debt issued		$ 300,000,000
Debt interest rate		6.375%
Proceeds from long-term debt, net of discounts		$ 293,800,000
Redemption price, percentage of principal amount of debt		100.00%
Term Loan Facility
Debt Instrument [Line Items]
Principal amount of debt issued	$ 415,000,000
Debt instrument, term	7 years
Line of Credit
Debt Instrument [Line Items]
Debt instrument, term	5 years
JP Morgan Chase Bank, N.A. | Credit Agreement
Debt Instrument [Line Items]
Minimum interest coverage ratio	2.75
JP Morgan Chase Bank, N.A. | Term Loan Facility
Debt Instrument [Line Items]
Principal amount of debt issued	$ 415,000,000
Debt instrument, term	7 years
Proceeds from issuance of debt	$ 408,700,000
Mandatory amortization payment, percent per annum	1.00%
Mandatory prepayments, percent of net cash proceeds	100.00%
Mandatory prepayments, percent of net cash proceeds, step down one	75.00%
Mandatory prepayments, percent of net cash proceeds, step down two	50.00%
Mandatory prepayment in excess of cash flow	50.00%
Mandatory prepayment in excess of cash flow, step down one	25.00%
Mandatory prepayment in excess of cash flow, step down two	0.00%
JP Morgan Chase Bank, N.A. | Line of Credit
Debt Instrument [Line Items]
Debt instrument, term	5 years
Maximum borrowing capacity	$ 250,000,000
Fiscal Quarter Ending June 30, 2019 | JP Morgan Chase Bank, N.A. | Credit Agreement
Debt Instrument [Line Items]
Maximum total leverage ratio	4
Fiscal Quarter Ending June 30, 2020 | JP Morgan Chase Bank, N.A. | Credit Agreement
Debt Instrument [Line Items]
Maximum total leverage ratio	3.75
After Fiscal Quarter Ending June 30, 2020 | JP Morgan Chase Bank, N.A. | Credit Agreement
Debt Instrument [Line Items]
Maximum total leverage ratio	3.50
Letter of Credit | JP Morgan Chase Bank, N.A. | Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 50,000,000

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			$ 1,635,285	$ 1,546,322	$ 1,546,322
Net transfer to/from Parent Company			(738,970)		(28,889)	$ (81,966)	$ (193,049)
Other comprehensive income (loss)	$ (76)	$ 5,370	(8,376)	7,094	7,214	1,065	(11,960)
Balance	962,547		962,547		1,635,285	1,546,322
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			(21,935)	(26,293)	(26,293)
Other comprehensive income (loss) before reclassifications, net of tax			(9,080)
Other comprehensive income (loss)			(9,080)
Balance	(31,015)		(31,015)		(21,935)	(26,293)
Defined Pension and Other Post-Retirement Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			(4,480)	(7,336)	(7,336)
Reclassification adjustment for cumulative effect of change in accounting principle	(1,315)		(1,315)
Net transfer to/from Parent Company			(2,421)
Other comprehensive income (loss) before reclassifications, net of tax			170
Reclassification adjustment for net losses (gains) included in net income, net of tax			534
Other comprehensive income (loss)			704
Balance	(7,512)		(7,512)		(4,480)	(7,336)
Accum. Other Comp. Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			(26,415)	$ (33,629)	(33,629)
Reclassification adjustment for cumulative effect of change in accounting principle	(1,315)		(1,315)
Net transfer to/from Parent Company			(2,421)
Other comprehensive income (loss) before reclassifications, net of tax			(8,910)
Reclassification adjustment for net losses (gains) included in net income, net of tax			534
Other comprehensive income (loss)			(8,376)		7,214	1,065	$ (11,960)
Balance	$ (38,527)		$ (38,527)		$ (26,415)	$ (33,629)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Loss - Reclassification Out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended											9 Months Ended				12 Months Ended
	Sep. 30, 2018		Dec. 31, 2017	Sep. 30, 2017		Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2018		Sep. 30, 2017		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial loss	$ (202,734)			$ (173,880)								$ (594,605)		$ (500,329)		$ (691,124)	$ (556,009)	$ (742,041)
Settlement loss	(69,022)			(54,828)								(194,568)		(162,359)		(219,517)	(205,409)	(245,723)
Income (loss) before income taxes	33,218			26,926								96,608		74,277		89,284	(18,834)	77,265
Tax benefit	(7,723)			(8,241)								(24,324)		(22,973)		22,284	8,043	(24,131)
Net income	25,263		$ 60,194	18,421		$ 18,754	$ 13,269	$ 3,769	$ (2,503)	$ (10,872)	$ (3,036)	71,989		50,444		110,638	(12,642)	51,698
Pension and other post-retirement benefit plans:
Net of tax	(439)	[1]		(67)	[1]							(704)	[1]	(199)	[1]	(2,856)	(112)	269
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial loss	116			100								243		299
Settlement loss	484											484
Income (loss) before income taxes	600			100								727		299
Tax benefit	(161)			(35)								(192)		(102)
Net income	$ 439			$ 65								$ 535		$ 197
Pension and other post-retirement benefit plans:
Amortization of actuarial losses and net transition obligation																397	362	340
Amortization of prior service costs																2	2	2
Total before tax																399	364	342
Tax benefit																(141)	(129)	(120)
Net of tax																$ 258	$ 235	$ 222
[1]	Net of income tax (expense) benefit of $161 and $35 for the three months ended September 30, 2018 and 2017, respectively, and $123 and $102 for the nine months ended September 30, 2018 and 2017, respectively.

Commitments and Contingencies_2

Commitments and Contingencies (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Letters of Credit Outstanding, Amount	$ 8,100	$ 16,045		$ 5,500
Total operating leases rental expense	$ 16,837	$ 17,936	$ 16,992

Revenue - Narrative (Detail)

Revenue - Narrative (Detail)	9 Months Ended
	Sep. 30, 2018
Long-term Contract with Customer [Member]
Disaggregation of Revenue [Line Items]
Contract term	1 year
Minimum [Member]
Disaggregation of Revenue [Line Items]
Payment terms	30 days
Maximum [Member]
Disaggregation of Revenue [Line Items]
Payment terms	90 days
Lease Revenue [Member]
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	3.00%
Other Revenue [Member]
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	1.00%
Product [Member] | Sales Revenue, Net [Member]
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	89.00%
Service [Member] | Sales Revenue, Net [Member]
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	7.00%

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended									9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disaggregation of Revenue [Line Items]
Revenue	$ 316,468	$ 264,498	$ 258,654	$ 256,161	$ 230,278	$ 201,176	$ 185,455	$ 168,535	$ 196,171	$ 906,318	$ 745,093	$ 1,009,591	$ 751,337	$ 1,076,680
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(10,797)		(10,877)							(32,163)	(29,160)	(36,103)	(35,669)	(39,959)
United States [Member]
Disaggregation of Revenue [Line Items]
Revenue	252,747									713,373		769,928	559,266	808,549
Canada [Member]
Disaggregation of Revenue [Line Items]
Revenue	20,759									58,639		79,186	54,714	64,961
Middle East [Member]
Disaggregation of Revenue [Line Items]
Revenue	13,645									40,091		48,899	54,767	69,951
Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	7,625									27,805		28,112	19,935	34,970
Latin America [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,364									25,097		34,368	23,588	23,208
Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,715									13,900
Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	9,613									27,413
Drilling Technologies [Member]
Disaggregation of Revenue [Line Items]
Revenue	75,254		59,200							209,727	166,664	227,653	113,320	164,297
Production and Automation Technologies [Member]
Disaggregation of Revenue [Line Items]
Revenue	241,214		$ 199,454							696,591	$ 578,429	$ 781,938	$ 638,017	$ 912,383
Production and Automation Technologies [Member] | Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(285)									(2,244)
Production and Automation Technologies [Member] | Artificial Lift Technologies [Member]
Disaggregation of Revenue [Line Items]
Revenue	188,005									544,566
Production and Automation Technologies [Member] | Automation Technologies [Member]
Disaggregation of Revenue [Line Items]
Revenue	31,114									85,347
Production and Automation Technologies [Member] | Other Production Equipment [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 22,380									$ 68,922

Revenue - Contract Balances (De

Revenue - Contract Balances (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018
Revenue from Contract with Customer [Abstract]
Contract assets	$ 3,475	$ 4,733
Contract liabilities - current	$ 6,827	$ 4,487

Restructuring and Other Relat_3

Restructuring and Other Related Charges (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ (39)	$ 8	$ 2,473	$ 21	$ 6,921	$ 15,162	$ 21,230
Cost of Goods and Services [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	(33)	(16)	1,557	(17)	6,332	9,465	9,095
Selling, General and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ (6)	$ 24	$ 916	$ 38	$ 589	$ 5,697	$ 12,135

Restructuring and Other Relat_4

Restructuring and Other Related Charges - Narrative (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 1,500		$ 1,500		$ 2,551	$ 459	$ 1,887	$ 95
Restructuring charges	$ (39)	$ 8	$ 2,473	$ 21	6,921	15,162	21,230
Production and Automation Technologies [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges					6,921	12,757	18,750
Drilling Technologies [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges					$ 0	$ 2,405	$ 2,480

Income Taxes (Detail)

Income Taxes (Detail) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 21, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Line Items]
Effective tax rate (as a percent)	23.20%	30.60%	25.20%	30.90%		(25.00%)		42.70%	31.20%
Effective Income Tax Rate, Federal Statutory Income Tax Rate (as a percent)			21.00%			35.00%	35.00%	35.00%	35.00%
Non Us Carry forwards loss						$ 1,280,000		$ 1,082,000
Provisional tax Benefits						53,200,000
Repatriation of provisional amount						3,900,000
Uncertain tax Position						0		$ 0
Scenario, Plan [Member]
Income Tax Disclosure [Line Items]
Effective Income Tax Rate, Federal Statutory Income Tax Rate (as a percent)					21.00%
Non-US [Member]
Income Tax Disclosure [Line Items]
Non Us Carry forwards loss						5,000,000
Non Us Carry forwards loss						$ 4,900,000
Tax Expiration Period						2028 through 2038
Cash Distribution to Subsidiary						$ 6,000,000
Operating Loss Carryforwards Indefinitely [Member] | Non-US [Member]
Income Tax Disclosure [Line Items]
Non Us Carry forwards loss						$ 100,000

Fair Value Measurements (Detail

Fair Value Measurements (Detail) - USD ($)	Sep. 30, 2018	May 09, 2018	May 03, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of debt issued		$ 715,000,000
Senior Notes | 6.375% Senior Notes Due May 2026
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of debt issued			$ 300,000,000
Senior Notes | 6.375% Senior Notes Due May 2026 | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of debt issued	$ 300,000,000
Debt, fair value	308,600,000
Term Loan Facility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of debt issued		$ 415,000,000
Term Loan Facility | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of debt issued	395,000,000
Debt, fair value	$ 397,000,000

Equity and Cash Incentive Pro_3

Equity and Cash Incentive Program - Narrative (Detail) - USD ($)	Dec. 31, 2017	May 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares authorized			6,500,000
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restrictions lapse period				2 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restrictions lapse period				3 years
Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years	3 years
Expiration period			10 years	10 years
SARs granted				82,240	106,548	98,803
Pricing model				Black-Scholes
Unrecognized compensation expense	$ 672,000			$ 672,000
Weighted Average period for Unrecognized compensation expense period				1 year 8 months 12 days
Performance Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
SARs granted		87,000		4,162
Share Based Compensation Arrangement				3 years
Stock Compensation Vesting shares				4,162	5,764	4,503
Unvested Performance Based Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	0			$ 0
Weighted Average period for Unrecognized compensation expense period				1 year
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
SARs granted		352,000		25,557	42,117	17,263
Unvested Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 2,060			$ 2,060
Weighted Average period for Unrecognized compensation expense period	1 year 7 months 6 days

Equity and Cash Incentive Pro_4

Equity and Cash Incentive Program - Share-based Compensation Expense Relating to All Stock-Based Incentive Plans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Based Compensation Expense [Abstract]
Stock-based compensation expense	$ 1,768	$ 630	$ 3,129	$ 1,762	$ 2,236	$ 2,293	$ 1,925
Tax benefit	(421)	(219)	(717)	(611)	(774)	(787)	(658)
Stock-based compensation expense, net of tax	$ 1,347	$ 411	$ 2,412	$ 1,151	$ 1,462	$ 1,506	$ 1,267

Employee Benefit Plans - Narrat

Employee Benefit Plans - Narrative (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 09, 2018	Jan. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Liabilities recognized at the Separation									$ 6,100
Accumulated other comprehensive loss recognized at the Separation			$ 2,400
Net periodic benefit cost	$ 1,100	$ 1,200	2,900	$ 3,500
Defined Contribution Plans expense	$ 2,500	$ 2,100	$ 7,200	$ 6,100		$ 8,150	$ 6,446	$ 7,247
Accumulated benefit obligation						$ 18,078	$ 22,112
Percentage of return on invested assets						5.50%	5.75%
Non-U.S. Qualified Defined Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost						$ 114	$ 104	122
Funded (unfunded) status						112	(121)			$ 112
Accumulated benefit obligation							3,512			$ 3,881
Dover Us Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employers' contribution to pension plan						0	0	0
Employers' future contribution to pension plan						0
Canada Salaried Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employers' contribution to pension plan						1,800	$ 2,000	$ 1,100
Employers' future contribution to pension plan						$ 0
Scenario, Forecast [Member] | Non-U.S. Qualified Defined Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost					$ 56
Contributions to the defined pension plan					$ 200

Segment Information (Detail)

Segment Information (Detail) - USD ($) $ in Thousands		3 Months Ended											9 Months Ended				12 Months Ended
		Sep. 30, 2018		Dec. 31, 2017	Sep. 30, 2017		Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2018		Sep. 30, 2017		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Reconciliation from Segment Totals to Consolidated [Abstract]
Revenue		$ 316,468		$ 264,498	$ 258,654		$ 256,161	$ 230,278	$ 201,176	$ 185,455	$ 168,535	$ 196,171	$ 906,318		$ 745,093		$ 1,009,591		$ 751,337		$ 1,076,680
Reconciliation of Earnings from Continuing Operations from Segments to Consolidated [Abstract]
Net income attributable to noncontrolling interest		232			264								295		860		930		1,851		1,436
Earnings before provision for income taxes		33,218			26,926								96,608		74,277		89,284		(18,834)		77,265
Depreciation and amortization:
Depreciation and amortization																	111,879		112,055		119,992
Restructuring charges:
Restructuring charges		(39)			8								2,473		21		6,921		15,162		21,230
Capital expenditures:
Capital Expenditure																	26,688		25,725		24,217
Total assets
Assets		1,983,356		1,904,775					1,850,895				1,983,356				1,904,775		1,850,895
Production and Automation Technologies [Member]
Reconciliation from Segment Totals to Consolidated [Abstract]
Revenue		241,214			199,454								696,591		578,429		781,938		638,017		912,383
Reconciliation of Earnings from Continuing Operations from Segments to Consolidated [Abstract]
Earnings before provision for income taxes		24,257			8,403								57,957		26,247		24,889	[1]	(21,687)	[1]	58,446	[1]
Depreciation and amortization:
Depreciation and amortization	[2]																99,929		99,607		103,612
Restructuring charges:
Restructuring charges																	6,921		12,757		18,750
Capital expenditures:
Capital Expenditure																	18,517		21,588		19,272
Total assets
Assets				1,683,782					1,659,711								1,683,782		1,659,711
Drilling Technologies [Member]
Reconciliation from Segment Totals to Consolidated [Abstract]
Revenue		75,254			59,200								209,727		166,664		227,653		113,320		164,297
Reconciliation of Earnings from Continuing Operations from Segments to Consolidated [Abstract]
Earnings before provision for income taxes		26,209			20,420								71,738		55,067		74,317		8,397		26,819
Depreciation and amortization:
Depreciation and amortization	[3],[4]																11,950		12,448		16,380
Restructuring charges:
Restructuring charges																	0		2,405		2,480
Capital expenditures:
Capital Expenditure																	8,171		4,137		4,945
Total assets
Assets				$ 220,993					$ 191,184								220,993		191,184
Total segments [Member]
Reconciliation of Earnings from Continuing Operations from Segments to Consolidated [Abstract]
Earnings before provision for income taxes		50,466			28,823								129,695		81,314		99,206		(13,290)		85,265
Corporate expense / other [Member]
Reconciliation of Earnings from Continuing Operations from Segments to Consolidated [Abstract]
Earnings before provision for income taxes		6,664	[5]		1,818	[5]							16,274	[5]	6,838	[5]	$ (10,852)	[6]	$ (7,395)	[6]	$ (9,436)	[6]
Interest Expense [Member]
Reconciliation of Earnings from Continuing Operations from Segments to Consolidated [Abstract]
Earnings before provision for income taxes		$ 10,584			$ 79								$ 16,813		$ 199
[1]	Segment operating profit (loss) for Production & Automation Technologies excludes the net income attributable to noncontrolling interest.
[2]	Depreciation and amortization expense for Production & Automation Technologies includes acquisition-related depreciation and amortization of $57,426, $60,025 and $63,217 for the years ended December 31, 2017, 2016 and 2015, respectively.
[3]	Depreciation and amortization expense for Drilling Technologies includes acquisition-related depreciation and amortization of $24, $115 and $3,010 for the years ended December 31, 2017, 2016 and 2015, respectively.
[4]	Intercompany eliminations for the years ended December 31, 2017, 2016 and 2015 relate principally between the product groups automation technologies and artificial lift technologies.
[5]	Corporate expense includes costs not directly attributable or allocated to our reporting segments such as corporate executive management and other administrative functions, costs related to our Separation from Dover Corporation and the results attributable to our noncontrolling interest.
[6]	Corporate expenses include those costs not attributable to a particular business segment such as corporate executive management and other corporate administrative functions.

Condensed Consolidating Finan_3

Condensed Consolidating Financial Information - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2018	May 09, 2018	May 03, 2018
Principal amount of debt issued		$ 715,000,000
Senior Notes
Debt Instrument, Issuer	The payment obligations of which are fully and unconditionally guaranteed by certain 100-percent-owned subsidiaries of Apergy.
6.375% Senior Notes Due May 2026 | Senior Notes
Principal amount of debt issued			$ 300,000,000

Condensed Consolidating Finan_4

Condensed Consolidating Financial Information - Schedule of Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended									9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Income Statements, Captions [Line Items]
Lease and other revenue	$ 12,894		$ 6,657							$ 35,993	$ 19,093
Related party revenue			11								19
Total revenue	316,468	$ 264,498	258,654	$ 256,161	$ 230,278	$ 201,176	$ 185,455	$ 168,535	$ 196,171	906,318	745,093	$ 1,009,591	$ 751,337	$ 1,076,680
Cost of goods and services	202,734		173,880							594,605	500,329	691,124	556,009	742,041
Gross profit	113,734	73,703	84,774	84,630	75,360	61,012	47,254	32,610	54,452	311,713	244,764	318,467	195,328	334,639
Selling, general and administrative expense	69,022		54,828							194,568	162,359	219,517	205,409	245,723
Operating income (loss)												98,950	(10,081)	88,916
Interest expense, net	10,584		79							16,813	199
Other expense (income), net	910		2,941							3,724	7,929	9,666	8,753	11,651
Income (loss) before income taxes	33,218		26,926							96,608	74,277	89,284	(18,834)	77,265
Income (loss) before income taxes and equity in earnings (losses) of affiliates												89,284	(18,834)	77,265
Provision for (benefit from) income taxes	7,723		8,241							24,324	22,973	(22,284)	(8,043)	24,131
Income (loss) before equity in earnings (losses) of affiliates	25,495		18,685							72,284	51,304	111,568	(10,791)	53,134
Net income (loss)	25,495	60,264	18,685	19,033	13,586	4,167	(2,154)	(10,294)	(2,510)	72,284	51,304	111,568	(10,791)	53,134
Net income (loss) attributable to noncontrolling interest	232		264							295	860	930	1,851	1,436
Net income (loss) attributable to Apergy	25,263	$ 60,194	18,421	$ 18,754	$ 13,269	$ 3,769	$ (2,503)	$ (10,872)	$ (3,036)	71,989	50,444	110,638	(12,642)	51,698
Comprehensive income (loss) attributable to Apergy	25,187		23,791							63,613	57,538	117,852	(11,577)	39,738
Adjustment [Member]
Condensed Income Statements, Captions [Line Items]
Lease and other revenue	12,895		6,647							35,994	19,074
Apergy Corporation
Condensed Income Statements, Captions [Line Items]
Selling, general and administrative expense	87									1,588
Interest expense, net	10,491									16,494
Income (loss) before income taxes	(10,578)									(18,082)
Provision for (benefit from) income taxes	(2,575)									(4,217)
Income (loss) before equity in earnings (losses) of affiliates	(8,003)									(13,865)
Equity in earnings (losses) of affiliates	33,266		18,421							85,854	50,444
Equity in earnings (losses) of affiliates												110,638	(12,642)	51,698
Net income (loss)	25,263		18,421							71,989	50,444	110,638	(12,642)	51,698
Net income (loss) attributable to Apergy	25,263		18,421							71,989	50,444	110,638	(12,642)	51,698
Comprehensive income (loss) attributable to Apergy	25,187		23,791							63,613	57,538	117,852	(11,577)	39,738
Subsidiary guarantors
Condensed Income Statements, Captions [Line Items]
Lease and other revenue	12,531		6,296							34,855	17,501
Related party revenue	5,944		7,656							18,598	19,477
Total revenue	282,781		226,994							810,023	652,592	881,187	644,392	923,957
Cost of goods and services	175,718		148,389							515,005	425,792	586,519	459,465	604,715
Gross profit	107,063		78,605							295,018	226,800	294,668	184,927	319,242
Selling, general and administrative expense	63,470		50,448							176,733	149,145	200,839	183,892	220,897
Operating income (loss)												93,829	1,035	98,345
Interest expense, net	84		78							288	196
Other expense (income), net	(524)		2,816							1,872	7,611	9,429	8,550	10,606
Income (loss) before income taxes	44,033		25,263							116,125	69,848
Income (loss) before income taxes and equity in earnings (losses) of affiliates												84,400	(7,515)	87,739
Provision for (benefit from) income taxes	8,744		7,938							24,076	22,726	(10,680)	(2,750)	29,485
Income (loss) before equity in earnings (losses) of affiliates	35,289		17,325							92,049	47,122	95,080	(4,765)	58,254
Equity in earnings (losses) of affiliates	5,344		2,435							18,811	5,579
Equity in earnings (losses) of affiliates												22,110	(23,668)	(17,980)
Net income (loss)	40,633		19,760							110,860	52,701	117,190	(28,433)	40,274
Net income (loss) attributable to Apergy	40,633		19,760							110,860	52,701	117,190	(28,433)	40,274
Comprehensive income (loss) attributable to Apergy	39,904		20,195							110,214	53,055	120,042	(28,402)	39,594
Subsidiary non-guarantors
Condensed Income Statements, Captions [Line Items]
Lease and other revenue	364		351							1,139	1,573
Related party revenue	4,853		3,232							13,565	9,702
Total revenue	44,484		42,537							128,458	121,661	164,507	142,614	192,682
Cost of goods and services	37,899		36,261							111,142	103,259	140,516	132,350	177,504
Gross profit	6,585		6,276							17,316	18,402	23,991	10,264	15,178
Selling, general and administrative expense	5,465		4,380							16,247	13,214	18,678	21,517	24,826
Operating income (loss)												5,313	(11,253)	(9,648)
Interest expense, net	9		1							32	3
Other expense (income), net	1,434		124							1,851	318	237	203	(376)
Income (loss) before income taxes	(323)		1,771							(814)	4,867
Income (loss) before income taxes and equity in earnings (losses) of affiliates												5,076	(11,456)	(9,272)
Provision for (benefit from) income taxes	1,536		340							4,595	400	(11,537)	(5,341)	(5,431)
Income (loss) before equity in earnings (losses) of affiliates	(1,859)		1,431							(5,409)	4,467	16,613	(6,115)	(3,841)
Equity in earnings (losses) of affiliates	12,604		3,006							37,568	5,446
Equity in earnings (losses) of affiliates												11,020	(8,273)	2,762
Net income (loss)	10,745		4,437							32,159	9,913	27,633	(14,388)	(1,079)
Net income (loss) attributable to noncontrolling interest	232		264							295	860	930	1,851	1,436
Net income (loss) attributable to Apergy	10,513		4,173							31,864	9,053	26,703	(16,239)	(2,515)
Comprehensive income (loss) attributable to Apergy	11,166		9,108							24,134	15,793	31,065	(15,205)	(13,795)
Product [Member]
Condensed Income Statements, Captions [Line Items]
Revenue	283,103		235,848							808,311	679,837
Product [Member] | Adjustment [Member]
Condensed Income Statements, Captions [Line Items]
Revenue	283,102									808,310
Product [Member] | Subsidiary guarantors
Condensed Income Statements, Captions [Line Items]
Revenue	250,549		203,623							714,226	590,554
Product [Member] | Subsidiary non-guarantors
Condensed Income Statements, Captions [Line Items]
Revenue	32,553		32,225							94,084	89,283
Service [Member]
Condensed Income Statements, Captions [Line Items]
Revenue	20,471		16,149							62,014	46,163
Service [Member] | Adjustment [Member]
Condensed Income Statements, Captions [Line Items]
Revenue			16,148
Service [Member] | Subsidiary guarantors
Condensed Income Statements, Captions [Line Items]
Revenue	13,757		9,419							42,344	25,060
Service [Member] | Subsidiary non-guarantors
Condensed Income Statements, Captions [Line Items]
Revenue	6,714		6,729							19,670	21,103
Intersegment Eliminations
Condensed Income Statements, Captions [Line Items]
Related party revenue	(10,797)		(10,877)							(32,163)	(29,160)
Total revenue	(10,797)		(10,877)							(32,163)	(29,160)	(36,103)	(35,669)	(39,959)
Cost of goods and services	(10,883)		(10,770)							(31,542)	(28,722)	(35,911)	(35,806)	(40,178)
Gross profit	86		(107)							(621)	(438)	(192)	137	219
Operating income (loss)												(192)	137	219
Interest expense, net										(1)
Other expense (income), net			1							1			0	1,421
Income (loss) before income taxes	86		(108)							(621)	(438)
Income (loss) before income taxes and equity in earnings (losses) of affiliates												(192)	137	(1,202)
Provision for (benefit from) income taxes	18		(37)							(130)	(153)	(67)	48	77
Income (loss) before equity in earnings (losses) of affiliates	68		(71)							(491)	(285)	(125)	89	(1,279)
Equity in earnings (losses) of affiliates	(51,214)		(23,862)							(142,233)	(61,469)
Equity in earnings (losses) of affiliates												(143,768)	44,583	(36,480)
Net income (loss)	(51,146)		(23,933)							(142,724)	(61,754)	(143,893)	44,672	(37,759)
Net income (loss) attributable to Apergy	(51,146)		(23,933)							(142,724)	(61,754)	(143,893)	44,672	(37,759)
Comprehensive income (loss) attributable to Apergy	$ (51,070)		$ (29,303)							$ (134,348)	$ (68,848)	$ (151,102)	$ 43,607	$ (25,799)

Condensed Consolidating Finan_5

Condensed Consolidating Financial Information - Schedule of Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 18,014	$ 23,712	$ 23,447	$ 26,027	$ 10,417	$ 24,355
Receivables	277,926	202,024		139,485
Inventories	219,133	201,591		184,558
Prepaid and other current assets	20,824	14,038		6,251
Total current assets	535,897	441,365		356,321
Property, plant and equipment, net	236,067	211,832		201,747
Goodwill	906,766	910,088		902,579	901,928
Intangible assets, net	297,397	338,510		386,817
Other assets and deferred charges	7,229	2,980		3,431
Total assets	1,983,356	1,904,775		1,850,895
Current liabilities:
Accounts payable	127,103	98,826		66,280
Accrued compensation and employee benefits	36,988	30,289		24,788
Other accrued expenses	53,054	21,950		21,626
Total current liabilities	217,145	151,065		112,694
Long-term debt	687,543	3,742
Deferred income taxes	93,138	96,985		167,565
Other long-term liabilities	20,770	12,949
Other liabilities including long term debt		16,691		19,283
Total liabilities	1,018,596	264,741
Equity:
Parent Company investment in Apergy	1,001,074	1,661,700		1,579,951
Accumulated other comprehensive loss	(38,527)	(26,415)		(33,629)
Total Parent Company equity	962,547	1,635,285		1,546,322
Noncontrolling interest	2,213	4,749		5,031
Total equity	964,760	1,640,034		1,551,353	1,644,993	1,797,040
Total liabilities and equity	1,983,356	1,904,775		1,850,895
Apergy Corporation
Current assets:
Cash and cash equivalents	108
Prepaid and other current assets	71
Total current assets	179
Advances due from affiliates	660,836
Investment in subsidiaries	978,944	1,640,034		1,551,353
Other assets and deferred charges	4,226
Total assets	1,644,185	1,640,034		1,551,353
Current liabilities:
Accounts payable	30
Other accrued expenses	(3,811)
Total current liabilities	(3,781)
Long-term debt	683,206
Total liabilities	679,425
Equity:
Parent Company investment in Apergy	964,760	1,640,034		1,551,353
Total Parent Company equity	964,760	1,640,034		1,551,353
Total equity	964,760	1,640,034		1,551,353
Total liabilities and equity	1,644,185	1,640,034		1,551,353
Subsidiary guarantors
Current assets:
Cash and cash equivalents	8,308	5,763	3,126	3,730	2,719	11,212
Receivables	245,950	171,363		116,340
Inventories	189,536	175,031		161,314
Prepaid and other current assets	18,846	11,990		4,090
Total current assets	462,640	364,147		285,474
Property, plant and equipment, net	222,425	195,579		180,292
Goodwill	633,771	633,734		633,734
Advances due from affiliates	14,228	10,299		10,464
Intercompany notes receivable	1,394
Investment in subsidiaries	688,890	801,235		753,916
Intangible assets, net	207,694	234,795		273,127
Other assets and deferred charges	2,292	2,129		2,499
Total assets	2,233,334	2,241,918		2,139,506
Current liabilities:
Accounts payable	113,497	83,864		53,195
Accrued compensation and employee benefits	31,619	24,875		20,450
Other accrued expenses	784,752	74,393		81,402
Total current liabilities	929,868	183,132		155,047
Intercompany notes payable	4
Long-term debt	4,321
Deferred income taxes	73,089	75,075		125,490
Other long-term liabilities	19,459
Other liabilities including long term debt		16,657		19,009
Total liabilities	1,026,741
Equity:
Parent Company investment in Apergy	1,213,290	1,971,790		1,847,548
Accumulated other comprehensive loss	(6,697)	(4,736)		(7,588)
Total Parent Company equity	1,206,593	1,967,054		1,839,960
Total equity	1,206,593	1,967,054		1,839,960
Total liabilities and equity	2,233,334	2,241,918		2,139,506
Subsidiary non-guarantors
Current assets:
Cash and cash equivalents	9,598	17,949	$ 20,321	22,297	$ 7,698	$ 13,143
Receivables	40,797	34,335		29,511
Inventories	31,146	27,488		23,979
Prepaid and other current assets	1,907	2,048		2,161
Total current assets	83,448	81,820		77,948
Property, plant and equipment, net	13,642	16,253		21,455
Goodwill	272,995	276,354		268,845
Advances due from affiliates	81,199	60,109		64,521
Intercompany notes receivable	4
Investment in subsidiaries	542,462	388,315		348,046
Intangible assets, net	89,703	103,715		113,690
Other assets and deferred charges	711	851		932
Total assets	1,084,164	927,417		895,437
Current liabilities:
Accounts payable	22,397	18,636		19,451
Accrued compensation and employee benefits	5,369	5,414		4,338
Other accrued expenses	28,703	18,289		15,466
Total current liabilities	56,469	42,339		39,255
Intercompany notes payable	1,394
Long-term debt	16
Deferred income taxes	20,049	21,910		42,075
Other long-term liabilities	1,311
Other liabilities including long term debt		34		274
Total liabilities	79,239
Equity:
Parent Company investment in Apergy	1,034,542	880,064		834,843
Accumulated other comprehensive loss	(31,830)	(21,679)		(26,041)
Total Parent Company equity	1,002,712	858,385		808,802
Noncontrolling interest	2,213	4,749		5,031
Total equity	1,004,925	863,134		813,833
Total liabilities and equity	1,084,164	927,417		895,437
Intersegment Eliminations
Current assets:
Receivables	(8,821)	(3,674)		(6,366)
Inventories	(1,549)	(928)		(735)
Total current assets	(10,370)	(4,602)		(7,101)
Advances due from affiliates	(756,263)	(70,408)		(74,985)
Intercompany notes receivable	(1,398)
Investment in subsidiaries	(2,210,296)	(2,829,584)		(2,653,315)
Total assets	(2,978,327)	(2,904,594)		(2,735,401)
Current liabilities:
Accounts payable	(8,821)	(3,674)		(6,366)
Other accrued expenses	(756,590)	(70,732)		(75,242)
Total current liabilities	(765,411)	(74,406)		(81,608)
Intercompany notes payable	(1,398)
Total liabilities	(766,809)
Equity:
Parent Company investment in Apergy	(2,211,518)	(2,830,188)		(2,653,793)
Total Parent Company equity	(2,211,518)	(2,830,188)		(2,653,793)
Total equity	(2,211,518)	(2,830,188)		(2,653,793)
Total liabilities and equity	$ (2,978,327)	$ (2,904,594)		$ (2,735,401)

Condensed Consolidating Finan_6

Condensed Consolidating Financial Information - Schedule of Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided (required) by operating activities	$ 92,806	$ 41,205	$ 76,917	$ 129,709	$ 215,671
Cash provided (required) by investing activities:
Additions to property, plant and equipment	(45,832)	(29,445)	(41,211)	(26,854)	(31,985)
Proceeds from sale of property, plant, and equipment	970	2,616	3,547	2,526	7,884
Purchase price adjustments on acquisition	53
Acquisition (net of cash and cash equivalents acquired)			(8,842)	(3,700)	(10,000)
Net cash provided (required) by investing activities	(44,809)	(26,829)	(46,506)	(28,028)	(34,101)
Cash provided (required) by financing activities:
Proceeds from long-term debt, net of discounts	713,963
Change in borrowings, net			(599)
Payment of debt issue costs	(16,006)
Repayments of long-term debt	(20,000)
Net transfers to Parent Company and intercompany distributions	(728,857)	(19,220)	(31,192)	(84,254)	(194,977)
Distribution to noncontrolling interest	(2,720)	(1,212)	(1,212)	(1,727)
Net cash provided by (required by) financing activities	(53,620)	(20,432)	(33,003)	(85,981)	(194,977)
Effect of exchange rate changes on cash and cash equivalents	(75)	3,476	277	(90)	(531)
Net decrease in cash and cash equivalents	(5,698)	(2,580)	(2,315)	15,610	(13,938)
Cash and cash equivalents at beginning of period	23,712	26,027	26,027	10,417	24,355
Cash and cash equivalents at end of period	18,014	23,447	23,712	26,027	10,417
Apergy Corporation
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided (required) by operating activities	(16,694)
Cash provided (required) by financing activities:
Proceeds from long-term debt, net of discounts	713,963
Payment of debt issue costs	(16,006)
Repayments of long-term debt	(20,000)
Advances due to/(from) affiliates	(660,836)
Net transfers to Parent Company and intercompany distributions	(319)
Net cash provided by (required by) financing activities	16,802
Net decrease in cash and cash equivalents	108
Cash and cash equivalents at end of period	108
Subsidiary guarantors
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided (required) by operating activities	103,911	38,153	65,289	103,788	137,352
Cash provided (required) by investing activities:
Additions to property, plant and equipment	(43,746)	(28,221)	(39,565)	(23,080)	(30,750)
Proceeds from sale of property, plant, and equipment	938	2,596	3,433	2,245	3,814
Acquisition (net of cash and cash equivalents acquired)				(3,700)	(10,000)
Net cash provided (required) by investing activities	(42,808)	(25,625)	(36,132)	(24,535)	(36,936)
Cash provided (required) by financing activities:
Advances due to/(from) affiliates	677,999
Net transfers to Parent Company and intercompany distributions	(736,557)	(13,132)	(27,124)	(78,232)	(108,909)
Net cash provided by (required by) financing activities	(58,558)	(13,132)	(27,124)	(78,232)	(108,909)
Net decrease in cash and cash equivalents	2,545	(604)	2,033	1,011	(8,493)
Cash and cash equivalents at beginning of period	5,763	3,730	3,730	2,719	11,212
Cash and cash equivalents at end of period	8,308	3,126	5,763	3,730	2,719
Subsidiary non-guarantors
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided (required) by operating activities	6,588	2,899	11,561	25,979	79,817
Cash provided (required) by investing activities:
Additions to property, plant and equipment	(2,086)	(1,224)	(1,646)	(3,774)	(1,235)
Proceeds from sale of property, plant, and equipment	32	20	114	281	4,070
Purchase price adjustments on acquisition	53
Acquisition (net of cash and cash equivalents acquired)			(8,842)
Net cash provided (required) by investing activities	(2,001)	(1,204)	(10,374)	(3,493)	2,835
Cash provided (required) by financing activities:
Change in borrowings, net			(599)
Advances due to/(from) affiliates	(17,163)
Net transfers to Parent Company and intercompany distributions	7,020	(5,935)	(4,001)	(6,070)	(87,566)
Distribution to noncontrolling interest	(2,720)	(1,212)	(1,212)	(1,727)
Net cash provided by (required by) financing activities	(12,863)	(7,147)	(5,812)	(7,797)	(87,566)
Effect of exchange rate changes on cash and cash equivalents	(75)	3,476	277	(90)	(531)
Net decrease in cash and cash equivalents	(8,351)	(1,976)	(4,348)	14,599	(5,445)
Cash and cash equivalents at beginning of period	17,949	22,297	22,297	7,698	13,143
Cash and cash equivalents at end of period	9,598	20,321	17,949	22,297	7,698
Intersegment Eliminations
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided (required) by operating activities	(999)	153	67	(48)	(1,498)
Cash provided (required) by financing activities:
Advances due to/(from) affiliates	999
Net transfers to Parent Company and intercompany distributions		(153)	(67)	48	1,498
Distribution to noncontrolling interest	$ 999
Net cash provided by (required by) financing activities		$ (153)	$ (67)	$ 48	$ 1,498

Summary of Significant Accoun_2

Summary of Significant Accounting Policies - Additional Information (Detail) $ / Occurrence_Per_Year in Millions	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2018	Dec. 31, 2017USD ($)Segment$ / Occurrence_Per_Year	Dec. 21, 2017	Dec. 31, 2016USD ($)$ / Occurrence_Per_Year	Dec. 31, 2015USD ($)
Organization And Significant Accounting Policies [Line Items]
Number of reportable segments | Segment					2
Related party transaction, selling, general and administrative expenses from transactions with related party	$ 4,700,000	$ 7,400,000	$ 16,500,000		$ 22,987,000		$ 19,459,000	$ 20,852,000
LIFO and valuation adjustments					10,556,000		9,381,000
Impairment Of indefinite-lived assets					$ 0		$ 0	$ 0
Percentage of Controlling interest					60.00%
Revenue recognition based on percentage of completion method					0.70%		2.50%	2.20%
Effective Income Tax Rate, Federal Statutory Income Tax Rate (as a percent)		21.00%			35.00%	35.00%	35.00%	35.00%
Research and development expense					$ 18,501,000		$ 16,511,000	$ 19,255,000
Advertising Expense					1,220,000		825,000	1,604,000
Scenario, Plan [Member]
Organization And Significant Accounting Policies [Line Items]
Effective Income Tax Rate, Federal Statutory Income Tax Rate (as a percent)				21.00%
Selling, General and Administrative Expenses [Member]
Organization And Significant Accounting Policies [Line Items]
Amortization expenses					$ 42,900,000		$ 45,200,000	$ 48,300,000
Software Standalone and Software-enabled tangible products [Member]
Organization And Significant Accounting Policies [Line Items]
Revenue recognition					8.10%		8.70%	8.70%
Service [Member]
Organization And Significant Accounting Policies [Line Items]
Revenue recognition					6.30%		6.80%	5.20%
Lease [Member]
Organization And Significant Accounting Policies [Line Items]
Revenue recognition					1.90%		2.70%	2.60%
Product and Commercial [Member]
Organization And Significant Accounting Policies [Line Items]
Self insurance | $ / Occurrence_Per_Year					5		5
Vehicles [Member]
Organization And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives					P3Y
Minimum [Member]
Organization And Significant Accounting Policies [Line Items]
Other intangible asset, useful life					5 years
Minimum [Member] | Buildings and improvements [Member]
Organization And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives					P5Y
Minimum [Member] | Machinery, equipment and other [Member]
Organization And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives					P3Y
Minimum [Member] | Furniture and Fixtures [Member]
Organization And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives					P3Y
Minimum [Member] | Software Development [Member]
Organization And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives					P3Y
Maximum [Member]
Organization And Significant Accounting Policies [Line Items]
Other intangible asset, useful life					15 years
Maximum [Member] | Automobile Loan [Member]
Organization And Significant Accounting Policies [Line Items]
Self insurance					$ 1,000,000		$ 1,000,000
Maximum [Member] | Workers Compensation [Member]
Organization And Significant Accounting Policies [Line Items]
Self insurance					$ 800,000		$ 800,000
Maximum [Member] | Buildings and improvements [Member]
Organization And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives					P31Y6M
Maximum [Member] | Machinery, equipment and other [Member]
Organization And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives					P7Y
Maximum [Member] | Furniture and Fixtures [Member]
Organization And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives					P7Y
Maximum [Member] | Software Development [Member]
Organization And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives					P10Y

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands	Oct. 02, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2018
Business Acquisition [Line Items]
Total consideration, net		$ 8,842	$ 3,700	$ 10,000
Goodwill		910,088	$ 902,579	$ 901,928	$ 906,766
Business Acquisition, Intangible Assets		$ 4,538
PCP Oil Tools S.A. and Ener Tools S.A. ("PCP") [Member]
Business Acquisition [Line Items]
Business Acquisition	Oct. 2, 2017
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Total consideration, net	$ 8,842
Goodwill	5,053
Business Acquisition, Intangible Assets	$ 4,538
Finite-Lived Intangible Assets, Remaining Amortization Period	9 years

Inventories - Additional Inform

Inventories - Additional Information (Detail)	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Percentage of LIFO Inventory	28.00%	32.00%

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets - Additional Information (Detail) $ in Thousands	Oct. 01, 2017USD ($)Reporting_Unit	Dec. 31, 2017USD ($)Reporting_Unit	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2018USD ($)
Goodwill And Other Intangible Assets [Line Items]
Goodwill discount rate			10.00%	10.50%
Goodwill		$ 910,088	$ 910,088	$ 902,579	$ 901,928	$ 906,766
Business Acquisition, Intangible Assets		$ 4,538	4,538
Total amortization			53,701	55,987	59,161
Drilling And Production And Dover Energy Automation [Member]
Goodwill And Other Intangible Assets [Line Items]
Number of reporting units | Reporting_Unit	2
Production And Automation Technologies And Drilling Technologies [Member]
Goodwill And Other Intangible Assets [Line Items]
Number of reporting units | Reporting_Unit		2
Drilling and Production [Member]
Goodwill And Other Intangible Assets [Line Items]
Goodwill	$ 733,641
Fair values excess in carrying values	90.00%
Dover Energy Automation [Member]
Goodwill And Other Intangible Assets [Line Items]
Goodwill	$ 172,480
Fair values excess in carrying values	233.00%
Production and Automation Technologies [Member]
Goodwill And Other Intangible Assets [Line Items]
Goodwill	$ 804,985	$ 808,952	808,952	801,443	800,792	805,630
Fair values excess in carrying values	69.00%
Drilling Technologies [Member]
Goodwill And Other Intangible Assets [Line Items]
Goodwill	$ 101,136	$ 101,136	$ 101,136	$ 101,136	$ 101,136	$ 101,136
Fair values excess in carrying values	464.00%

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets - Estimated Future Amortization Expense related to Intangible Assets (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Estimated future amortization
2,018	$ 52,357
2,019	51,509
2,020	50,059
2,021	49,231
2,022	$ 47,683

Other Accrued Expenses and Ot_3

Other Accrued Expenses and Other Liabilities - Components of Other Accrued Expenses (Current) (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Other accrued expenses
Unearned/deferred revenue		$ 4,487	$ 3,787
Warranty		2,978	4,568
Restructuring and exit costs		2,551	459
Taxes other than income		2,432	1,424
Accrued freight, travel and transportation		1,397	1,384
Short-term capital lease obligations		1,041	694
Accrued rebates		617	473
Other (none of which are individually significant)		6,447	8,837
Total other accrued expenses	$ 53,054	$ 21,950	$ 21,626

Other Accrued Expenses and Ot_4

Other Accrued Expenses and Other Liabilities - Components of Other Liabilities (Noncurrent) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other liabilities
Defined benefit and other post-retirement benefit plans	$ 12,650	$ 16,510
Long-term capital lease obligations	3,742	1,919
Warranty	92	98
Other (none of which are individually significant)	207	756
Total other liabilities	$ 16,691	$ 19,283

Other Accrued Expenses and Ot_5

Other Accrued Expenses and Other Liabilities - Carrying Amount of Product Warranties (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance, beginning of year	$ 4,666	$ 4,421	$ 6,717
Provision for warranties	309	2,109	1,266
Settlements made	(1,896)	(1,518)	(3,168)
Other adjustments, including currency translation	(9)	(346)	(394)
Balance, end of year	$ 3,070	$ 4,666	$ 4,421

Restructuring Activities - Rest

Restructuring Activities - Restructuring and Other Related Charges (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ (39)	$ 8	$ 2,473	$ 21	$ 6,921	$ 15,162	$ 21,230
Production and Automation Technologies [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges					6,921	12,757	18,750
Drilling Technologies [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges					$ 0	$ 2,405	$ 2,480

Restructuring Activities - Comp

Restructuring Activities - Company's Severance and Other Restructuring Accrual Activities (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Reserve [Roll Forward]
Balance				$ 2,551	$ 459	$ 459	$ 1,887	$ 95
Restructuring charges		$ (39)	$ 8	2,473	21	6,921	15,162	21,230
Payments						(1,378)	(13,645)	(12,144)
Other, including foreign currency translation	[1]					(3,451)	(2,945)	(7,294)	[2]
Balance		$ 1,500		1,500		2,551	459	1,887
Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Balance					250	250	1,164	95
Restructuring charges						151	10,496	9,366
Payments						(400)	(11,235)	(8,197)
Other, including foreign currency translation	[1]					(1)	(175)	(100)	[2]
Balance							250	1,164
Spinoff [Member]
Restructuring Reserve [Roll Forward]
Balance				$ 2,551	$ 209	209	723
Restructuring charges						6,770	4,666	11,864
Payments						(978)	(2,410)	(3,947)
Other, including foreign currency translation	[1]					(3,450)	(2,770)	(7,194)	[2]
Balance						$ 2,551	$ 209	$ 723
[1]	Other activity in exit reserves primarily represents the non-cash write-off of long-lived assets and inventory in connection with certain facility closures and exit of certain nonstrategic product lines.
[2]	Segment operating profit (loss) includes certain corporate expenses that are allocated to the segments such as information technology, supply chain, and shared services based on direct benefit where identifiable or other methods which the Company believes to be a reasonable reflection of the utilization of services provided.

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income before Income Tax, Domestic and Foreign (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic					$ 66,852	$ (25,926)	$ 61,670
Foreign					22,432	7,092	15,595
Income (loss) before income taxes	$ 33,218	$ 26,926	$ 96,608	$ 74,277	$ 89,284	$ (18,834)	$ 77,265

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
U.S. federal					$ 42,312	$ 8,872	$ 40,415
State and local					4,230	1,995	(332)
Foreign					6,176	971	5,344
Total current					52,718	11,838	45,427
Deferred:
U.S. federal					(73,544)	(19,161)	(23,135)
State and local					(1,361)	(771)	4,141
Foreign					(97)	51	(2,302)
Total deferred			$ (4,674)	$ (17,503)	(75,002)	(19,881)	(21,296)
Total (benefit) expense	$ 7,723	$ 8,241	$ 24,324	$ 22,973	$ (22,284)	$ (8,043)	$ 24,131

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 21, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
U.S. federal income tax rate			21.00%		35.00%	35.00%	35.00%	35.00%
State and local taxes, net of federal income tax benefit					2.10%		(3.90%)	3.10%
Foreign operations tax effect					(2.80%)		7.80%	(3.10%)
Research and experimentation tax credits					(0.70%)		2.30%	(0.70%)
Domestic manufacturing deduction					(4.50%)		6.20%	(4.60%)
Nondeductible expenses					0.70%		(3.30%)	1.00%
ESOP dividends					(0.20%)		2.90%	(0.70%)
Branch income					1.10%		(2.90%)	0.80%
Changes due to the Tax Reform Act					(55.20%)
Other					(0.50%)		(1.40%)	0.40%
Effective tax rate from continuing operations	23.20%	30.60%	25.20%	30.90%	(25.00%)		42.70%	31.20%

Income Taxes - Schedule of Futu

Income Taxes - Schedule of Future Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018
Deferred Tax Assets:
Accrued compensation, principally post-retirement and other employee benefits	$ 4,568	$ 9,126
Accrued expenses, principally for state income taxes, interest and warranty	846	1,512
Net operating loss and other carryforwards	1,280	1,082
Accounts receivable, principally due to allowance for doubtful accounts	827	1,780
Long-term liabilities, principally warranty, environmental and exit cost	678	620
Other assets	132	459
Total gross deferred tax assets	8,331	14,579
Valuation allowance	(1,280)	(1,082)
Total deferred tax assets, net of valuation allowances	7,051	13,497
Deferred Tax Liabilities:
Inventories, principally due to reserves for financial reporting purposes and capitalization for tax purposes	(3,687)	(4,754)
Intangible assets, principally due to different tax and financial reporting bases and amortization lives	(83,669)	(149,500)
Property, plant and equipment, principally due to differences in depreciation	(16,134)	(26,254)
Total gross deferred tax liabilities	(103,490)	(180,508)
Net deferred tax liability	(96,439)	(167,011)
Classified as follows in the Combined Balance Sheets:
Other assets and deferred charges	546	554
Deferred income taxes	(96,985)	(167,565)	$ (93,138)
Net deferred tax liability	$ (96,439)	$ (167,011)

Equity and Cash Incentive Pro_5

Equity and Cash Incentive Program - Black Scholes Option-Pricing Model (Detail) - Stock Appreciation Rights [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.80%	1.05%	1.51%
Dividend yield	2.27%	3.09%	2.24%
Expected life (years)	4 years 7 months 6 days	4 years 7 months 6 days	5 years 1 month 6 days
Volatility	21.90%	26.17%	27.19%
Grant price	$ 79.28	$ 57.25	$ 73.28
Fair value at date of grant	$ 12.63	$ 9.25	$ 14.55

Equity and Cash Incentive Pro_6

Equity and Cash Incentive Program - Summary of Activity Relating to SARs (Detail) - Stock Appreciation Rights [Member]	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Number of SARs
Number of Shares Outstanding, Beginning Balance | shares	454,683
Number of Shares, Granted | shares	82,240
Number of Shares, Forfeited or expired | shares	(32,944)
Number of Shares, Exercised | shares	(116,908)
Number of Shares Outstanding, Ending Balance | shares	387,071
Number of Shares Exercisable | shares	157,078
Weighted-Average Exercise Price
Weighted Average Exercise Price, Beginning Balance | $ / shares	$ 63.69
Weighted Average Exercise Price, Granted | $ / shares	79.28
Weighted Average Exercise Price, Forfeited or expired | $ / shares	67.1
Weighted Average Exercise Price, Exercised | $ / shares	61.93
Weighted Average Exercise Price, Ending Balance | $ / shares	67.17
Weighted Average Exercise Price Exercisable | $ / shares	$ 64.3
Weighted-Average Remaining Contractual Term (Years)
Weighted Average Contractual Term, Outstanding	6 years 8 months 12 days
Weighted Average Contractual Term, Exercisable	4 years 7 months 6 days

Equity And Cash Incentive Pro_7

Equity And Cash Incentive Program - Summary of Outstanding and Exercisable SARs (Detail) - Stock Appreciation Rights [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding	387,071	454,683
Weighted Average Remaining Life in Years	6 years 8 months 12 days
Aggregate Intrinsic Value, Outstanding	$ 13,089
Number of Shares, Exercisable	157,078
Weighted Average Exercise Price	$ 64.3
Weighted Average Remaining Life in Years	4 years 7 months 6 days
Aggregate Intrinsic Value, Exercisable	$ 5,763
Range of Exercise Price $25.96 - $37.79 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding	23,816
Weighted Average Exercise Price	$ 37.79
Weighted Average Remaining Life in Years	2 years 1 month 6 days
Aggregate Intrinsic Value, Outstanding	$ 1,505
Number of Shares, Exercisable	23,816
Weighted Average Exercise Price	$ 37.79
Weighted Average Remaining Life in Years	2 years 1 month 6 days
Aggregate Intrinsic Value, Exercisable	$ 1,505
Range of Exercise Price $40.54 - $58.69 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding	125,469
Weighted Average Exercise Price	$ 57.52
Weighted Average Remaining Life in Years	6 years 8 months 12 days
Aggregate Intrinsic Value, Outstanding	$ 5,454
Number of Shares, Exercisable	38,309
Weighted Average Exercise Price	$ 58.14
Weighted Average Remaining Life in Years	3 years 7 months 6 days
Aggregate Intrinsic Value, Exercisable	$ 1,642
Range of Exercise Price $63.33 - $82.51 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding	237,786
Weighted Average Exercise Price	$ 75.21
Weighted Average Remaining Life in Years	7 years 2 months 12 days
Aggregate Intrinsic Value, Outstanding	$ 6,130
Number of Shares, Exercisable	94,953
Weighted Average Exercise Price	$ 73.44
Weighted Average Remaining Life in Years	5 years 8 months 12 days
Aggregate Intrinsic Value, Exercisable	$ 2,616

Equity and Cash Incentive Pro_8

Equity and Cash Incentive Program - Other Information Regarding Exercise of SARs and Stock Options (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value	$ 1,239	$ 1,564	$ 1,356
Aggregate intrinsic value	$ 2,787	$ 799	1,874
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash received from exercise of stock options			100
Aggregate intrinsic value			$ 117

Equity and Cash Incentive Pro_9

Equity and Cash Incentive Program - Fair Value Used in Determining Compensation Cost of Performance Shares (Detail) - Performance Share Awards [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value per share at date of grant	$ 79.28	$ 57.25	$ 73.28
Average attainment rate reflected in expense	0.00%	0.00%	0.00%

Equity and Cash Incentive Pr_10

Equity and Cash Incentive Program - Summary of Activity for Performance Share Awards (Detail) - Performance Share Awards [Member] - $ / shares	1 Months Ended	12 Months Ended
	May 31, 2018	Dec. 31, 2017
Number of Shares
Number of Shares, Unvested, Beginning Balance		10,267
Number of Shares, Granted	87,000	4,162
Number of Shares, Vested		(4,503)
Number of Shares, Unvested, Ending Balance		9,926
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning Balance		$ 64.28
Weighted Average Grant Date Fair Value, Granted		79.28
Weighted Average Grant Date Fair Value, Vested		73.28
Weighted Average Grant Date Fair Value, Ending Balance		$ 66.49

Equity and Cash Incentive Pr_11

Equity and Cash Incentive Program - Summary of activity for restricted stock units (Detail) - Restricted Stock Units (RSUs) [Member]	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Number of Shares
Number of Shares, Unvested, Beginning Balance | shares	54,064
Number of Shares, Granted | shares	25,557
Number of Shares, Forfeited | shares	(8,854)
Number of Shares, Vested | shares	(20,712)
Number of Shares, Unvested, Ending Balance | shares	50,055
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning Balance | $ / shares	$ 61.68
Weighted Average Grant Date Fair Value, Granted | $ / shares	79.28
Weighted Average Grant Date Fair Value, Forfeited | $ / shares	64.07
Weighted Average Grant Date Fair Value, Vested | $ / shares	64.85
Weighted Average Grant Date Fair Value, Ending Balance | $ / shares	$ 68.91

Commitments and Contingent Liab

Commitments and Contingent Liabilities - Operating And Capital Leases (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 11,668
2,019	10,646
2,020	7,639
2,021	5,309
2,022	4,625
Thereafter	5,105
Total	44,992
2,018	2,232
2,019	1,696
2,020	181
2,021	0
2,022	0
Thereafter	0
Total	$ 4,109

Employee Benefit Plans And No_3

Employee Benefit Plans And Non-Qualified Plans - Summary of Expenses Recorded in the Financial Statements (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Dover Us Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan expenses	$ 3,922	$ 4,643	$ 4,783
Canada Salaried Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan expenses	554	1,615	513
Other non-qualified Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan expenses	$ 108	$ 121	$ 123

Employee Benefit Plans and No_4

Employee Benefit Plans and Non-Qualified Plans - Summary of Combined Balance Sheets Impact Associated with the Company's Single Employer Defined Benefit Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Jan. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Other assets and deferred charges	$ 546		$ 554
Accumulated benefit obligations	18,078		22,112
Non-U.S. Qualified Defined Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	3,512	$ 3,512	3,139
Service cost	106	106	102	$ 118
Interest cost	137	137	129	130
Benefits paid		(99)	(79)
Actuarial loss (gain)		(22)	170
Currency translation and other		247	51
Benefit obligation at end of year		3,881	3,512	3,139
Fair value of plan assets at beginning of year	3,391	3,391	3,056
Actual return on plan assets		290	198
Company contributions		166	165
Benefits paid		(99)	(79)
Currency translation and other		245	51
Fair value of plan assets at end of year	3,993	3,993	3,391	3,056
Funded (unfunded) status	112	112	(121)
Other assets and deferred charges		112
Other liabilities			(121)
Total assets and liabilities		112	(121)
Net actuarial losses		1,449	1,632
Prior service cost		40	42
Net asset at transition, other		(20)	(21)
Deferred taxes		(397)	(446)
Total accumulated other comprehensive loss, net of tax		1,072	1,207
Net amount recognized at December 31,		1,184	1,086
Accumulated benefit obligations		3,881	3,512
Non Qualified Supplemental Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	18,600	18,600	20,313
Interest cost	$ 621	621	719	708
Benefits paid		(1,710)	(2,484)
Actuarial loss (gain)		(3,314)	52
Benefit obligation at end of year		14,197	18,600	$ 20,313
Company contributions		1,710	2,484
Benefits paid		(1,710)	(2,484)
Funded (unfunded) status		(14,197)	(18,600)
Accrued compensation and employee benefits		(1,547)	(2,211)
Other liabilities		(12,650)	(16,389)
Total assets and liabilities		(14,197)	(18,600)
Net actuarial losses		6,078	9,721
Deferred taxes		(2,670)	(3,592)
Total accumulated other comprehensive loss, net of tax		3,408	6,129
Net amount recognized at December 31,		(10,789)	(12,471)
Accumulated benefit obligations		$ 14,197	$ 18,600

Employee Benefit Plans and No_5

Employee Benefit Plans and Non-Qualified Plans - Summary of Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets (Detail) $ in Thousands	Dec. 31, 2016USD ($)
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Projected benefit obligation (PBO)	$ 3,512
Accumulated benefit obligation (ABO)	3,512
Fair value of plan assets	$ 3,391

Employee Benefit Plans and No_6

Employee Benefit Plans and Non-Qualified Plans - Components of the Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Jan. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Total	$ 1,100	$ 1,200	$ 2,900	$ 3,500
Non-U.S. Qualified Defined Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost					$ 106	$ 106	$ 102	$ 118
Interest cost					137	137	129	130
Expected return on plan assets					(198)		(186)	(184)
Prior service cost					2		2	2
Recognized actuarial loss					68		58	57
Transition obligation					(1)		(1)	(1)
Total					114		104	122
Non Qualified Supplemental Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost					621	$ 621	719	708
Recognized actuarial loss					330		305	284
Other					(1)
Total					$ 950		$ 1,024	$ 992

Employee Benefit Plans and No_7

Employee Benefit Plans and Non-Qualified Plans - Schedule of Amounts Expected to be Amortized from Accumulated Other Comprehensive Income (loss) into Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Total	$ 1,100	$ 1,200	$ 2,900	$ 3,500
Non-U.S. Qualified Defined Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						$ 2	$ 2	$ 2
Transition obligation						(1)	(1)	(1)
Total						114	104	122
Non-U.S. Qualified Defined Benefit Plan [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost					$ 2
Recognized actuarial loss					55
Transition obligation					(1)
Total					56
Non Qualified Supplemental Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total						$ 950	$ 1,024	$ 992
Non Qualified Supplemental Benefit Plan [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Recognized actuarial loss					205
Total					$ 205

Employee Benefit Plans and No_8

Employee Benefit Plans and Non-Qualified Plans - Weighted Average Assumptions Used in Determining the Benefit Obligations (Detail)	Dec. 31, 2017	Dec. 31, 2016
Non-U.S. Qualified Defined Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.50%	3.75%
Non Qualified Supplemental Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.35%	3.55%

Employee Benefit Plans and No_9

Employee Benefit Plans and Non-Qualified Plans - Weighted Average Assumptions Used in Determining the Net Periodic Benefit Cost (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Non-U.S. Qualified Defined Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.75%	4.00%
Expected return on plan assets	5.50%	5.75%
Non Qualified Supplemental Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.55%	3.75%

Employee Benefit Plans and N_10

Employee Benefit Plans and Non-Qualified Plans - Actual and Target Weighted Average Asset Allocation (Detail) - Non Us Corporate Pension Plan [Member]	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual allocations of pension plans	100.00%	100.00%
Target allocations of pension plans	100.00%
Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual allocations of pension plans	61.00%	60.00%
Target allocations of pension plans	60.00%
Lease [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual allocations of pension plans	38.00%	39.00%
Target allocations of pension plans	40.00%
Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual allocations of pension plans	1.00%	1.00%

Employee Benefit Plans and N_11

Employee Benefit Plans and Non-Qualified Plans - Fair Values of Pension Plan Assets by Asset Category within the Fair Value Hierarchy (Detail) - Non-U.S. Qualified Defined Benefit Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Jan. 31, 2017	Dec. 31, 2016	Jan. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 3,993	$ 3,993	$ 3,391	$ 3,391	$ 3,056
Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,993		3,391
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,399		2,104
Fair Value, Inputs, Level 1 | Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,399		2,104
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,594		1,287
Fair Value, Inputs, Level 2 | Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,594		$ 1,287

Employee Benefit Plans and N_12

Employee Benefit Plans and Non-Qualified Plans - Estimated Future Benefit Payments to Retirees (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Non-U.S. Qualified Defined Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,018	$ 86
2,019	94
2,020	92
2,021	100
2,022	107
2023 - 2027	709
Non Qualified Supplemental Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,018	1,572
2,019	1,472
2,020	1,368
2,021	1,261
2,022	1,154
2023 - 2027	$ 4,163

Other Comprehensive Income (Los

Other Comprehensive Income (Loss) - Schedule of Amounts Recognized in Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended				12 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Foreign currency translation adjustments, before tax									$ 4,358	$ 953	$ (11,691)
Pension and other post-retirement benefit plans, before tax									3,827	154	(393)
Total other comprehensive income (loss, before tax									8,185	1,107	(12,084)
Foreign currency translation adjustments, tax	$ 0		$ 0		$ 0		$ 0		0	0	0
Pension and other post-retirement benefit plans, tax	(161)		(35)		(123)		(102)		(971)	(42)	124
Total other comprehensive (loss) income, tax									(971)	(42)	124
Foreign currency translation adjustments, net of tax									4,358	953	(11,691)
Pension and other post-retirement benefit plans, net of tax	439	[1]	67	[1]	704	[1]	199	[1]	2,856	112	(269)
Other comprehensive income (loss)	$ (76)		$ 5,370		$ (8,376)		$ 7,094		$ 7,214	$ 1,065	$ (11,960)
[1]	Net of income tax (expense) benefit of $161 and $35 for the three months ended September 30, 2018 and 2017, respectively, and $123 and $102 for the nine months ended September 30, 2018 and 2017, respectively.

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) - Schedule of Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended									9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net income (loss) attributable to Apergy	$ 25,263	$ 60,194	$ 18,421	$ 18,754	$ 13,269	$ 3,769	$ (2,503)	$ (10,872)	$ (3,036)	$ 71,989	$ 50,444	$ 110,638	$ (12,642)	$ 51,698
Other comprehensive income (loss)	(76)		5,370							(8,376)	7,094	7,214	1,065	(11,960)
Comprehensive income (loss)	$ 25,187		$ 23,791							$ 63,613	$ 57,538	$ 117,852	$ (11,577)	$ 39,738

Segment Information - Additiona

Segment Information - Additional Information (Detail)	3 Months Ended
	Dec. 31, 2017Segment
Segment Reporting [Abstract]
Number of Operating Segments	2

Segment Information (Parentheti

Segment Information (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Production and Automation Technologies [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization expense	$ 57,426	$ 60,025	$ 63,217
Drilling Technologies [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization expense	$ 24	$ 115	$ 3,010

Segment Information - Revenue C

Segment Information - Revenue Classified by Significant Products and Services (Detail) - USD ($) $ in Thousands		3 Months Ended									9 Months Ended		12 Months Ended
		Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue
Revenues		$ 316,468	$ 264,498	$ 258,654	$ 256,161	$ 230,278	$ 201,176	$ 185,455	$ 168,535	$ 196,171	$ 906,318	$ 745,093	$ 1,009,591	$ 751,337	$ 1,076,680
Artificial Lift Technologies [Member]
Revenue
Revenues													601,412	499,033	693,311
Automation Technologies [Member]
Revenue
Revenues													82,093	65,351	93,639
Other Production Equipment [Member]
Revenue
Revenues													103,564	75,182	126,870
Drilling Technologies [Member]
Revenue
Revenues		$ 75,254		$ 59,200							$ 209,727	$ 166,664	227,653	113,320	164,297
Inter Company Eliminations [Member]
Revenue
Revenues	[1]												$ (5,131)	$ (1,549)	$ (1,437)
[1]	Intercompany eliminations for the years ended December 31, 2017, 2016 and 2015 relate principally between the product groups automation technologies and artificial lift technologies.

Segment Information - Informati

Segment Information - Information Concerning Principal Geographic Areas (Detail) - USD ($) $ in Thousands	3 Months Ended									9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Combined total	$ 316,468	$ 264,498	$ 258,654	$ 256,161	$ 230,278	$ 201,176	$ 185,455	$ 168,535	$ 196,171	$ 906,318	$ 745,093	$ 1,009,591	$ 751,337	$ 1,076,680
Long Lived Assets		211,832				201,747						211,832	201,747
United States [Member]
Segment Reporting Information [Line Items]
Combined total	252,747									713,373		769,928	559,266	808,549
Long Lived Assets		198,178				184,268						198,178	184,268
Middle East [Member]
Segment Reporting Information [Line Items]
Combined total	13,645									40,091		48,899	54,767	69,951
Long Lived Assets		5,189				8,417						5,189	8,417
Canada [Member]
Segment Reporting Information [Line Items]
Combined total	20,759									58,639		79,186	54,714	64,961
Long Lived Assets		7,587				8,214						7,587	8,214
Europe [Member]
Segment Reporting Information [Line Items]
Combined total	7,625									27,805		28,112	19,935	34,970
Australia [Member]
Segment Reporting Information [Line Items]
Combined total												23,667	18,177	47,811
Long Lived Assets		681				619						681	619
Latin America [Member]
Segment Reporting Information [Line Items]
Combined total	$ 8,364									$ 25,097		34,368	23,588	23,208
Long Lived Assets		$ 197				$ 229						197	229
Other Countries [Member]
Segment Reporting Information [Line Items]
Combined total												$ 25,431	$ 20,890	$ 27,230

Pro Forma Information (unaudi_2

Pro Forma Information (unaudited) - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unaudited Pro Forma Information [Abstract]
Net transfers to Parent	$ (728,857)	$ (19,220)	$ (31,192)	$ (84,254)	$ (194,977)
Par value of common stock (in dollars per share)	$ 0.01
Common stock, shares issued (in shares)	77.3
Pro Forma
Unaudited Pro Forma Information [Abstract]
Net transfers to Parent			700,000
Disttribution using Proceeds from the incurrence			$ 702,500
Par value of common stock (in dollars per share)			$ 0.01
Common stock, shares issued (in shares)			77.4

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail)	May 09, 2018USD ($)shares	May 03, 2018USD ($)	Sep. 30, 2018USD ($)
Subsequent Event [Line Items]
Number of companies separated	2
Common stock issued (in shares) | shares	77,339,828
Conversion ratio	0.5
Principal amount of debt issued	$ 715,000,000
Business separation payment	700,000,000	$ 700,000,000
Proceeds from long-term debt, net of discounts			$ 713,963,000
Registration right agreement term, point before annual interest rate increase		1 year
Term Loan Facility
Subsequent Event [Line Items]
Principal amount of debt issued	$ 415,000,000
Debt instrument, term	7 years
Line of Credit
Subsequent Event [Line Items]
Debt instrument, term	5 years
6.375% Senior Notes Due May 2026 | Senior Notes
Subsequent Event [Line Items]
Principal amount of debt issued		$ 300,000,000
Debt interest rate		6.375%
Proceeds from long-term debt, net of discounts		$ 293,800,000
6.375% Senior Notes Due May 2026 | 6.375% Senior Notes Due May 2026
Subsequent Event [Line Items]
Debt interest rate		6.375%
Proceeds from long-term debt, net of discounts		$ 293,800,000

Quarterly Information - Busines

Quarterly Information - Business Information Segment (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Segment Information [Abstract]
Revenue	$ 316,468	$ 264,498		$ 258,654		$ 256,161		$ 230,278		$ 201,176		$ 185,455		$ 168,535		$ 196,171		$ 906,318	$ 745,093	$ 1,009,591	$ 751,337	$ 1,076,680
Gross profit	113,734	73,703		84,774		84,630		75,360		61,012		47,254		32,610		54,452		311,713	244,764	318,467	195,328	334,639
Net income (loss)	25,495	60,264		18,685		19,033		13,586		4,167		(2,154)		(10,294)		(2,510)		72,284	51,304	111,568	(10,791)	53,134
Net income (loss) attributable to Apergy	$ 25,263	$ 60,194		$ 18,421		$ 18,754		$ 13,269		$ 3,769		$ (2,503)		$ (10,872)		$ (3,036)		$ 71,989	$ 50,444	$ 110,638	$ (12,642)	$ 51,698
Basic earnings per share	$ 0.33	$ 0.78	[1]	$ 0.24	[1]	$ 0.24	[1]	$ 0.17	[1]	$ 0.05	[1]	$ (0.03)	[1]	$ (0.14)	[1]	$ (0.04)	[1]	$ 0.93	$ 0.65
Diluted earnings per share	$ 0.33	$ 0.77	[1]	$ 0.24	[1]	$ 0.24	[1]	$ 0.17	[1]	$ 0.05	[1]	$ (0.03)	[1]	$ (0.14)	[1]	$ (0.04)	[1]	$ 0.93	$ 0.65
[1]	On May 9, 2018, 77,339,828 shares of our common stock were distributed to Dover stockholders in conjunction with the Separation. For comparative purposes, we have assumed the shares issued in conjunction with the Separation to be outstanding as of the beginning of each period prior to the Separation. In addition, we have assumed the potential dilutive securities outstanding as of May 8, 2018, were outstanding and fully dilutive in each of the periods prior to the Separation.

Quarterly Information - Busin_2

Quarterly Information - Business Information Segment (Parenthetical) (Detail) - shares	Sep. 30, 2018	May 09, 2018
Segment Reporting Information [Line Items]
Common Stock,Shares Outstanding	77,300,000
Subsequent Event [Member]
Segment Reporting Information [Line Items]
Common Stock,Shares Outstanding		77,339,828

Schedule II - Schedule Of Valua

Schedule II - Schedule Of Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year		$ 5,634	$ 4,431	$ 3,510
Charged to Cost and Expense	[1]	954	2,941	2,154
Acounts Written Off		(1,882)	(1,469)	(1,159)
Other		47	(269)	(74)
Balance at End of Year		4,753	5,634	4,431
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year		1,082	64	50
Additions		198	1,018	14
Balance at End of Year		1,280	1,082	64
SEC Schedule, 12-09, Reserve, Inventory [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year		9,381	12,933	15,214
Charged to Cost and Expense		1,175
Reductions			(3,552)	(2,281)
Balance at End of Year		$ 10,556	$ 9,381	$ 12,933
[1]	Net of recoveries on previously reserved or written-off balances.