|
Guarantees (Details) (USD $)
|
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
|
Jan. 31, 2015
|
Jan. 31, 2014
|
Jan. 31, 2015
|
Jan. 31, 2014
|
|
| Guarantor Obligations [Line Items] | ||||
| Contingent liability for standby letters of credit, issued and outstanding | $ 7,900,000 | $ 7,900,000 | ||
| Amount drawn upon letters of credit | 0 | 0 | ||
| Advanced Filtration Systems, Inc. [Member] | ||||
| Guarantor Obligations [Line Items] | ||||
| Outstanding debt of joint venture | 23,100,000 | 23,100,000 | ||
| Joint venture investment earnings | 600,000 | 700,000 | 1,500,000 | 1,300,000 |
| Royalty income | $ 1,500,000 | $ 1,800,000 | $ 3,100,000 | $ 3,300,000 |