Guarantees (Details) - USD ($) |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
Apr. 30, 2017 |
Apr. 30, 2016 |
Apr. 30, 2017 |
Apr. 30, 2016 |
Jul. 31, 2016 |
|
| Guarantor Obligations [Line Items] | |||||
| Contingent liability for standby letters of credit, issued and outstanding | $ 9,100,000 | $ 9,100,000 | $ 7,300,000 | ||
| Amount drawn upon letters of credit | 0 | 0 | |||
| Advanced Filtration Systems, Inc. | |||||
| Guarantor Obligations [Line Items] | |||||
| Outstanding debt of joint venture | 28,600,000 | 28,600,000 | |||
| Joint venture investment earnings (loss) | 700,000 | $ (200,000) | 1,600,000 | $ (1,000,000) | |
| Royalty income | $ 1,600,000 | $ 1,300,000 | $ 4,300,000 | $ 3,900,000 | |