Selected Quarterly Financial Data (Unaudited) - Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
	May 09, 2018	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenue		$ 247,748	$ 276,839	$ 306,170	$ 300,494	$ 313,133	$ 316,171	$ 305,747	$ 283,105	$ 1,131,251		$ 1,218,156		$ 1,010,466
Gross profit		72,634	92,699	108,760	103,011	106,595	112,327	104,090	93,992	377,104		417,004		320,068
Net income		(1,574)	11,588	23,008	19,938	23,347	24,015	21,879	23,950	52,960		93,191		110,519
Net income (loss) attributable to Apergy		$ (1,823)	$ 11,394	$ 22,937	$ 19,656	$ 23,187	$ 23,961	$ 21,816	$ 23,773	$ 52,164		$ 92,737		$ 109,589
Basic earnings per share attributable to Apergy (in dollars per share)		$ (0.02)	$ 0.15	$ 0.30	$ 0.25	$ 0.30	$ 0.31	$ 0.28	$ 0.31	$ 0.67	[1]	$ 1.20	[1]	$ 1.42	[1]
Diluted earnings per share attributable to Apergy (in dollars per share)		$ (0.02)	$ 0.15	$ 0.30	$ 0.25	$ 0.30	$ 0.31	$ 0.28	$ 0.31	$ 0.67	[1]	$ 1.19	[1]	$ 1.41	[1]
Issuance of common stock at the Separation (in shares)	77,339,828

[1] See Note 4—Earnings Per Share.