Shareholder Report, Line Graph (Details) - USD ($) |
May 31, 2025 |
Feb. 28, 2025 |
Nov. 30, 2024 |
Aug. 31, 2024 |
May 31, 2024 |
Feb. 29, 2024 |
Nov. 30, 2023 |
Aug. 31, 2023 |
May 31, 2023 |
Feb. 28, 2023 |
Nov. 30, 2022 |
Aug. 31, 2022 |
May 31, 2022 |
Feb. 28, 2022 |
Nov. 30, 2021 |
Aug. 31, 2021 |
May 31, 2021 |
Feb. 28, 2021 |
Nov. 30, 2020 |
Aug. 31, 2020 |
May 31, 2020 |
Feb. 29, 2020 |
Nov. 30, 2019 |
Aug. 31, 2019 |
May 31, 2019 |
Feb. 28, 2019 |
Nov. 30, 2018 |
Aug. 31, 2018 |
May 31, 2018 |
Feb. 28, 2018 |
Nov. 30, 2017 |
Aug. 31, 2017 |
May 31, 2017 |
Feb. 28, 2017 |
Nov. 30, 2016 |
Aug. 31, 2016 |
May 31, 2016 |
Feb. 29, 2016 |
Nov. 30, 2015 |
Aug. 31, 2015 |
May 31, 2015 |
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| C000126665 | |||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||
| Account Value | $ 1,265,686 | $ 1,313,395 | $ 1,315,647 | $ 1,311,418 | $ 1,234,822 | $ 1,238,592 | $ 1,189,194 | $ 1,191,804 | $ 1,209,010 | $ 1,186,637 | $ 1,183,195 | $ 1,222,877 | $ 1,274,484 | $ 1,452,284 | $ 1,588,558 | $ 1,585,990 | $ 1,493,876 | $ 1,491,066 | $ 1,568,717 | $ 1,512,677 | $ 1,431,119 | $ 1,453,159 | $ 1,358,429 | $ 1,366,421 | $ 1,221,908 | $ 1,129,881 | $ 1,064,187 | $ 1,110,521 | $ 1,101,446 | $ 1,111,556 | $ 1,146,855 | $ 1,140,977 | $ 1,104,526 | $ 1,075,580 | $ 1,041,048 | $ 1,130,746 | $ 1,057,193 | $ 996,175 | $ 983,681 | $ 966,278 | $ 1,000,000 |
| Bloomberg U.S. Aggregate Bond Index | |||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||
| Account Value | 1,159,566 | 1,162,919 | 1,150,711 | 1,152,201 | 1,099,543 | 1,099,082 | 1,076,688 | 1,073,845 | 1,085,373 | 1,063,691 | 1,064,134 | 1,086,814 | 1,109,140 | 1,178,238 | 1,220,891 | 1,228,259 | 1,208,504 | 1,210,239 | 1,235,137 | 1,229,296 | 1,213,416 | 1,193,723 | 1,151,280 | 1,154,556 | 1,108,998 | 1,068,852 | 1,039,144 | 1,047,954 | 1,042,288 | 1,036,013 | 1,053,280 | 1,059,067 | 1,046,207 | 1,030,806 | 1,020,480 | 1,053,876 | 1,029,949 | 1,016,421 | 998,790 | 994,541 | 1,000,000 |
| Bloomberg U.S. Long Credit Bond Index | |||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||
| Account Value | $ 1,251,259 | $ 1,291,104 | $ 1,298,294 | $ 1,291,827 | $ 1,219,348 | $ 1,223,805 | $ 1,181,868 | $ 1,177,514 | $ 1,185,028 | $ 1,159,465 | $ 1,158,353 | $ 1,190,464 | $ 1,241,107 | $ 1,400,306 | $ 1,538,669 | $ 1,540,438 | $ 1,460,796 | $ 1,461,158 | $ 1,544,587 | $ 1,486,036 | $ 1,414,081 | $ 1,452,920 | $ 1,367,708 | $ 1,373,134 | $ 1,233,026 | $ 1,147,343 | $ 1,083,222 | $ 1,134,703 | $ 1,127,659 | $ 1,136,158 | $ 1,166,596 | $ 1,155,239 | $ 1,117,649 | $ 1,084,633 | $ 1,044,645 | $ 1,133,185 | $ 1,052,404 | $ 981,157 | $ 974,465 | $ 965,301 | $ 1,000,000 |