SCHEDULE I - Evoqua Water Technologies Corp. Condensed Consolidated Balance Sheets (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Condensed Financial Statements, Captions [Line Items]
Current assets	$ 637,293	$ 565,560
Cash and cash equivalents	109,881	82,365
Prepaid and other current assets	21,940	23,854
Total assets	1,737,848	1,663,617
Total liabilities	1,372,026	1,301,601
Common stock, par value $0.01: authorized 1,000,000 shares; issued 116,008 shares, outstanding 114,344 at September 30, 2019; issued 115,016, outstanding 113,929 shares at September 30, 2018	1,154	1,145
Treasury stock: 1,664 shares at September 30, 2019 and 1,087 shares at September 30, 2018	(2,837)	(2,837)
Additional paid‑in capital	552,422	533,435
Retained deficit	(174,976)	(163,871)
Total Evoqua Water Technologies Corp. equity	362,759	358,855
Total liabilities and shareholders’ equity	$ 1,737,848	$ 1,663,617
Common stock, par value (in USD per share)	$ 0.01	$ 0.01
Common stock authorized (in shares)	1,000,000,000	1,000,000,000
Common stock issued (in shares)	116,008,000	115,016,000
Common stock outstanding (in shares)	114,344,000	113,929,000
Treasury stock (in shares)	1,664,000	1,087,000
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Current assets	$ 335	$ 129
Cash and cash equivalents	121	76
Prepaid and other current assets	214	53
Investment in affiliate	385,175	376,555
Total assets	385,510	376,684
Due to affiliates	9,747	8,812
Total liabilities	9,747	8,812
Common stock, par value $0.01: authorized 1,000,000 shares; issued 116,008 shares, outstanding 114,344 at September 30, 2019; issued 115,016, outstanding 113,929 shares at September 30, 2018	1,154	1,145
Treasury stock: 1,664 shares at September 30, 2019 and 1,087 shares at September 30, 2018	(2,837)	(2,837)
Additional paid‑in capital	552,422	533,435
Retained deficit	(174,976)	(163,871)
Total Evoqua Water Technologies Corp. equity	375,763	367,872
Total liabilities and shareholders’ equity	$ 385,510	$ 376,684
Common stock, par value (in USD per share)	$ 0.01	$ 0.01
Common stock authorized (in shares)	1,000,000	1,000,000
Common stock issued (in shares)	116,008	115,016
Common stock outstanding (in shares)	114,344	113,929
Treasury stock (in shares)	1,664,000	410,000