Shareholder Report, Holdings (Details) - C000089187 [Member] |
Apr. 30, 2026 |
|---|---|
| BAA [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Moody's, Aaa Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.50% |
| Standard & Poor's, A Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.40% |
| Standard & Poor's, AA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 85.10% |
| Cash [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.20% |