Share-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		6 Months Ended
	Apr. 01, 2019	Dec. 21, 2018	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value, exercises in period					$ 2,923
Employee Stock Ownership Plan (ESOP), Shares in ESOP		11,297
Common stock, par value (in USD per share)			$ 0.01		$ 0.01		$ 0.01
Non-cash share-based compensation			$ 4,745	$ 4,250	$ 9,270	$ 6,862
Share-based Compensation expense			4,764		9,323
Compensation cost not yet recognized, period for recognition			$ 17,646		17,646
Fair value of options vested					$ 3,699
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number			1,197,000		1,197,000
Proceeds from issuance of common stock			$ 273	$ 0	$ 341	$ 137,605
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity incentive plan, number of shares authorized (shares)			5,100,000		5,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant			1,904,000		1,904,000
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity incentive plan, number of shares authorized (shares)			11,083,000		11,083,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant			1,704,000		1,704,000
Compensation cost not yet recognized, period for recognition			$ 11,594		$ 11,594
Period for recognition for unrecognized compensation expense			2 years 11 months
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period for recognition for unrecognized compensation expense			1 year 7 months
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number			2,054,000		2,054,000		1,213,000
Aggregate value			$ 25,000		$ 25,000
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock Ownership Plan (ESOP), Shares in ESOP		5,000
Common stock, par value (in USD per share)		$ 0.01
Employee Stock Ownership Plan (ESOP), Compensation Expense			$ 138		$ 293
Evoqua Water Technologies Corp. Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting percentage			25.00%
Expiration period			10 years
Subsequent Event [Member] | Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under ESPP	46,000