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 |
Feb. 22, 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 |
May 03, 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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| C000005564 | |||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||
| Account Value | $ 10,811 | $ 10,711 | $ 10,587 | $ 10,678 | $ 10,184 | $ 10,205 | $ 10,072 | $ 10,039 | $ 10,269 | $ 10,041 | $ 10,141 | $ 10,347 | $ 10,564 | $ 11,228 | $ 11,531 | $ 11,701 | $ 11,565 | $ 11,582 | $ 11,832 | $ 11,866 | $ 11,857 | $ 11,468 | $ 11,005 | $ 11,144 | $ 10,740 | $ 10,316 | $ 10,083 | $ 10,088 | $ 10,038 | $ 9,974 | $ 10,185 | $ 10,337 | $ 10,243 | $ 10,113 | $ 10,044 | $ 10,426 | $ 10,281 | $ 10,292 | $ 10,015 | $ 9,995 | $ 10,000 | ||
| C000190630 | |||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||
| Account Value | 537,873 | 532,589 | 525,170 | 530,391 | 505,666 | 506,480 | 498,703 | 497,884 | 508,063 | 497,552 | 502,331 | 512,328 | 522,836 | 555,480 | 570,245 | 577,492 | 571,495 | 572,097 | 583,311 | 585,704 | 584,148 | 565,677 | 541,765 | 548,426 | 528,356 | 508,174 | 496,518 | 495,675 | 493,013 | 490,572 | 500,743 | 508,052 | 504,112 | $ 500,000 | |||||||||
| C000225819 | |||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||
| Account Value | 9,385 | 9,290 | 9,176 | 9,247 | 8,813 | 8,825 | 8,704 | 8,670 | 8,862 | 8,660 | 8,757 | 8,912 | 9,093 | 9,657 | 9,911 | 10,051 | 9,928 | 9,952 | $ 10,000 | ||||||||||||||||||||||||
| Bloomberg U.S. Aggregate Bond Index | |||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||
| Account Value | 11,596 | 11,629 | 11,507 | 11,522 | 10,995 | 10,991 | 10,767 | 10,738 | 10,854 | 10,637 | 10,641 | 10,868 | 11,091 | 11,782 | 12,209 | 12,283 | 12,085 | 12,102 | 12,351 | 12,293 | 12,134 | 11,937 | 11,513 | 11,546 | 11,090 | 10,689 | 10,391 | 10,480 | 10,423 | 10,360 | 10,533 | 10,591 | 10,462 | 10,308 | 10,205 | 10,539 | 10,299 | 10,164 | 9,988 | 9,945 | 10,000 | ||
| Bloomberg U.S. Aggregate Bond Index | |||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||
| Account Value | 558,790 | 560,405 | 554,522 | 555,240 | 529,865 | 529,642 | 518,851 | 517,481 | 523,036 | 512,588 | 512,801 | 523,730 | 534,490 | 567,787 | 588,342 | 591,892 | 582,372 | 583,208 | 595,207 | 592,392 | 584,740 | 575,250 | 554,796 | 556,375 | 534,421 | 515,075 | 500,759 | 505,004 | 502,274 | 499,250 | 507,571 | 510,360 | 504,163 | 500,000 | |||||||||
| Bloomberg U.S. Aggregate Bond Index | |||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||
| Account Value | 9,571 | 9,598 | 9,498 | 9,510 | 9,075 | 9,071 | 8,887 | 8,863 | 8,958 | 8,779 | 8,783 | 8,970 | 9,154 | 9,725 | 10,077 | 10,138 | 9,975 | 9,989 | 10,000 | ||||||||||||||||||||||||
| Bloomberg U.S. 4-10 Year Treasury Bond Index | |||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||
| Account Value | 11,330 | 11,230 | 11,082 | 11,168 | 10,643 | 10,665 | 10,516 | 10,483 | 10,667 | 10,373 | 10,471 | 10,660 | 10,853 | 11,484 | 11,785 | 11,937 | 11,799 | 11,818 | 12,083 | 12,134 | 12,099 | 11,685 | 11,186 | 11,298 | 10,887 | 10,472 | 10,213 | 10,212 | 10,164 | 10,080 | 10,297 | 10,459 | 10,357 | $ 10,194 | $ 10,129 | $ 10,508 | $ 10,337 | $ 10,349 | $ 10,027 | $ 10,005 | $ 10,000 | ||
| Bloomberg U.S. 4-10 Year Treasury Bond Index | |||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||
| Account Value | 551,320 | 546,452 | 539,227 | 543,412 | 517,864 | 518,966 | 511,714 | 510,068 | 519,062 | 504,740 | 509,509 | 518,677 | 528,109 | 558,786 | 573,432 | 580,844 | 574,100 | 575,041 | $ 587,950 | $ 590,412 | $ 588,726 | $ 568,599 | $ 544,274 | $ 549,754 | $ 529,755 | $ 509,545 | $ 496,959 | $ 496,880 | $ 494,586 | $ 490,488 | $ 501,041 | $ 508,910 | $ 503,959 | $ 500,000 | |||||||||
| Bloomberg U.S. 4-10 Year Treasury Bond Index | |||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||
| Account Value | $ 9,538 | $ 9,453 | $ 9,328 | $ 9,401 | $ 8,959 | $ 8,978 | $ 8,852 | $ 8,824 | $ 8,980 | $ 8,732 | $ 8,814 | $ 8,973 | $ 9,136 | $ 9,667 | $ 9,920 | $ 10,048 | $ 9,932 | $ 9,948 | $ 10,000 |