Shareholder Report, Line Graph (Details) - USD ($) |
3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended | 15 Months Ended | 18 Months Ended | 21 Months Ended | 24 Months Ended | 27 Months Ended | 30 Months Ended | 33 Months Ended | 36 Months Ended | 39 Months Ended | 42 Months Ended | 45 Months Ended | 48 Months Ended | 51 Months Ended | 54 Months Ended | 57 Months Ended | 60 Months Ended | 63 Months Ended | 66 Months Ended | 69 Months Ended | 72 Months Ended | 75 Months Ended | 78 Months Ended | 81 Months Ended | 84 Months Ended | 87 Months Ended | 90 Months Ended | 93 Months Ended | 96 Months Ended | 99 Months Ended | 102 Months Ended | 105 Months Ended | 108 Months Ended | 111 Months Ended | 114 Months Ended | 117 Months Ended | 120 Months Ended | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Feb. 28, 2021 |
Feb. 22, 2021 |
May 31, 2016 |
May 31, 2021 |
Aug. 31, 2016 |
Aug. 31, 2021 |
Nov. 30, 2016 |
Nov. 30, 2021 |
Feb. 28, 2017 |
Feb. 28, 2022 |
May 31, 2017 |
May 31, 2022 |
Aug. 31, 2017 |
Aug. 31, 2022 |
Nov. 30, 2017 |
Nov. 30, 2022 |
Feb. 28, 2018 |
Feb. 28, 2023 |
May 31, 2018 |
May 31, 2023 |
Aug. 31, 2018 |
Aug. 31, 2023 |
Nov. 30, 2018 |
Nov. 30, 2023 |
Feb. 28, 2019 |
Feb. 29, 2024 |
May 31, 2019 |
May 31, 2024 |
Aug. 31, 2019 |
Aug. 31, 2024 |
Nov. 30, 2019 |
Nov. 30, 2024 |
Feb. 29, 2020 |
Feb. 28, 2025 |
May 31, 2020 |
May 31, 2025 |
Aug. 31, 2020 |
Aug. 31, 2025 |
Nov. 30, 2020 |
Nov. 30, 2025 |
Feb. 28, 2021 |
Feb. 28, 2026 |
May 31, 2021 |
May 31, 2026 |
Aug. 31, 2021 |
Nov. 30, 2021 |
Feb. 28, 2022 |
May 31, 2022 |
Aug. 31, 2022 |
Nov. 30, 2022 |
Feb. 28, 2023 |
May 31, 2023 |
Aug. 31, 2023 |
Nov. 30, 2023 |
Feb. 29, 2024 |
May 31, 2024 |
Aug. 31, 2024 |
Nov. 30, 2024 |
Feb. 28, 2025 |
May 31, 2025 |
Aug. 31, 2025 |
Nov. 30, 2025 |
Feb. 28, 2026 |
May 31, 2026 |
|
| C000005519 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | $ 10,000 | $ 10,390 | $ 9,952 | $ 10,170 | $ 10,382 | $ 10,575 | $ 10,585 | $ 10,384 | $ 10,302 | $ 10,382 | $ 10,154 | $ 10,586 | $ 11,071 | $ 11,739 | $ 11,780 | $ 12,252 | $ 11,831 | $ 12,372 | $ 12,662 | $ 12,436 | $ 12,465 | $ 12,852 | $ 12,694 | $ 11,996 | $ 11,109 | $ 10,730 | $ 10,561 | $ 10,633 | $ 10,840 | $ 10,805 | $ 10,931 | $ 11,265 | $ 11,363 | $ 11,923 | $ 11,987 | $ 12,101 | $ 12,007 | $ 12,397 | $ 12,694 | $ 12,835 | $ 12,733 | |||||||||||||||||||||||
| C000166313 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | 500,000 | 519,636 | 497,852 | 508,914 | 519,684 | 529,503 | 530,151 | 520,257 | 516,304 | 521,076 | 509,807 | 531,587 | 555,530 | 589,811 | 592,053 | 615,916 | 594,945 | 622,300 | 637,058 | 625,852 | 627,499 | 647,172 | 639,432 | 604,534 | 560,322 | 541,510 | 533,208 | 537,111 | 547,114 | 546,287 | 552,922 | 569,330 | 575,285 | 603,906 | 607,421 | 612,750 | 609,026 | 629,079 | 644,422 | 651,907 | 647,015 | |||||||||||||||||||||||
| C000225817 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | $ 9,965 | $ 10,000 | $ 10,014 | $ 10,330 | $ 10,217 | $ 9,679 | $ 8,970 | $ 8,688 | $ 8,563 | $ 8,624 | $ 8,804 | $ 8,789 | $ 8,916 | $ 9,190 | $ 9,284 | $ 9,756 | $ 9,822 | $ 9,931 | $ 9,880 | $ 10,202 | $ 10,461 | $ 10,593 | $ 10,524 | |||||||||||||||||||||||||||||||||||||||||
| Bloomberg U.S. Aggregate Bond Index | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | 10,000 | 10,232 | 9,908 | 10,008 | 10,158 | 10,283 | 10,227 | 10,059 | 10,120 | 10,175 | 10,089 | 10,378 | 10,768 | 11,210 | 11,178 | 11,590 | 11,781 | 11,936 | 11,992 | 11,750 | 11,734 | 11,925 | 11,854 | 11,440 | 10,769 | 10,552 | 10,332 | 10,328 | 10,538 | 10,426 | 10,454 | 10,671 | 10,676 | 11,187 | 11,173 | 11,291 | 11,258 | 11,538 | 11,809 | 11,998 | 11,836 | |||||||||||||||||||||||
| Bloomberg U.S. Aggregate Bond Index | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | 500,000 | 511,616 | 495,403 | 500,416 | 507,893 | 514,136 | 511,326 | 502,944 | 505,990 | 508,741 | 504,464 | 518,886 | 538,376 | 560,492 | 558,902 | 579,506 | 589,067 | 596,775 | 599,611 | 587,524 | 586,682 | 596,272 | 592,695 | 571,989 | 538,444 | 527,606 | 516,596 | 516,381 | 526,907 | 521,310 | 522,690 | 533,562 | 533,786 | 559,349 | 558,625 | 564,552 | 562,924 | 576,891 | 590,474 | 599,896 | 591,821 | |||||||||||||||||||||||
| Bloomberg U.S. Aggregate Bond Index | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | 9,989 | 10,000 | 9,975 | 10,138 | 10,077 | 9,725 | 9,154 | 8,970 | 8,783 | 8,779 | 8,958 | 8,863 | 8,887 | 9,071 | 9,075 | 9,510 | 9,498 | 9,598 | 9,571 | 9,808 | 10,039 | 10,199 | 10,062 | |||||||||||||||||||||||||||||||||||||||||
| Bloomberg U.S. Corporate Investment Grade Bond Index | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | 10,000 | 10,395 | 10,009 | 10,223 | 10,426 | 10,617 | 10,626 | 10,448 | 10,432 | 10,510 | 10,302 | 10,723 | 11,209 | 11,911 | 11,935 | 12,418 | 12,333 | 12,805 | 13,100 | 12,765 | 12,782 | 13,128 | 13,030 | 12,330 | 11,468 | 11,170 | 11,016 | 11,044 | 11,273 | 11,270 | 11,408 | 11,703 | 11,769 | 12,317 | 12,395 | 12,471 | 12,430 | 12,799 | 13,126 | 13,293 | 13,188 | |||||||||||||||||||||||
| Bloomberg U.S. Corporate Investment Grade Bond Index | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | $ 500,000 | $ 519,741 | $ 500,440 | $ 511,138 | $ 521,324 | $ 530,832 | $ 531,275 | $ 522,377 | $ 521,621 | $ 525,484 | $ 515,104 | $ 536,133 | $ 560,465 | $ 595,541 | $ 596,757 | $ 620,903 | $ 616,655 | $ 640,231 | $ 655,004 | $ 638,227 | $ 639,097 | $ 656,421 | $ 651,523 | $ 616,505 | $ 573,402 | $ 558,517 | $ 550,810 | $ 552,223 | $ 563,661 | $ 563,520 | $ 570,381 | $ 585,167 | $ 588,469 | $ 615,863 | $ 619,751 | $ 623,573 | $ 621,502 | $ 639,948 | $ 656,310 | $ 664,631 | $ 659,377 | |||||||||||||||||||||||
| Bloomberg U.S. Corporate Investment Grade Bond Index | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | $ 9,999 | $ 10,000 | $ 10,013 | $ 10,284 | $ 10,207 | $ 9,659 | $ 8,984 | $ 8,750 | $ 8,630 | $ 8,652 | $ 8,831 | $ 8,829 | $ 8,936 | $ 9,168 | $ 9,220 | $ 9,649 | $ 9,710 | $ 9,770 | $ 9,737 | $ 10,026 | $ 10,282 | $ 10,413 | $ 10,331 | |||||||||||||||||||||||||||||||||||||||||