Shareholder Report, Line Graph (Details) - USD ($) |
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Jul. 06, 2017 |
Feb. 29, 2016 |
Aug. 31, 2017 |
May 31, 2016 |
Nov. 30, 2017 |
Aug. 31, 2016 |
Feb. 28, 2018 |
Nov. 30, 2016 |
May 31, 2018 |
Feb. 28, 2017 |
Aug. 31, 2018 |
May 31, 2017 |
Nov. 30, 2018 |
Aug. 31, 2017 |
Feb. 28, 2019 |
Nov. 30, 2017 |
May 31, 2019 |
Feb. 28, 2018 |
Aug. 31, 2019 |
May 31, 2018 |
Nov. 30, 2019 |
Aug. 31, 2018 |
Feb. 29, 2020 |
Nov. 30, 2018 |
May 31, 2020 |
Feb. 28, 2019 |
Aug. 31, 2020 |
May 31, 2019 |
Nov. 30, 2020 |
Aug. 31, 2019 |
Feb. 28, 2021 |
Nov. 30, 2019 |
May 31, 2021 |
Feb. 29, 2020 |
Aug. 31, 2021 |
May 31, 2020 |
Nov. 30, 2021 |
Aug. 31, 2020 |
Feb. 28, 2022 |
Nov. 30, 2020 |
May 31, 2022 |
Feb. 28, 2021 |
Aug. 31, 2022 |
May 31, 2021 |
Nov. 30, 2022 |
Aug. 31, 2021 |
Feb. 28, 2023 |
Nov. 30, 2021 |
May 31, 2023 |
Feb. 28, 2022 |
Aug. 31, 2023 |
May 31, 2022 |
Nov. 30, 2023 |
Aug. 31, 2022 |
Feb. 29, 2024 |
Nov. 30, 2022 |
May 31, 2024 |
Feb. 28, 2023 |
Aug. 31, 2024 |
May 31, 2023 |
Nov. 30, 2024 |
Aug. 31, 2023 |
Feb. 28, 2025 |
Nov. 30, 2023 |
May 31, 2025 |
Feb. 29, 2024 |
Aug. 31, 2025 |
May 31, 2024 |
Nov. 30, 2025 |
Aug. 31, 2024 |
Feb. 28, 2026 |
Nov. 30, 2024 |
Feb. 28, 2025 |
May 31, 2025 |
Aug. 31, 2025 |
Nov. 30, 2025 |
Feb. 28, 2026 |
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| C000005541 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | $ 10,000 | $ 10,170 | $ 10,347 | $ 9,882 | $ 10,056 | $ 10,264 | $ 10,371 | $ 10,331 | $ 10,310 | $ 10,418 | $ 10,457 | $ 10,413 | $ 10,616 | $ 10,942 | $ 11,238 | $ 11,182 | $ 11,551 | $ 11,236 | $ 11,551 | $ 11,713 | $ 11,694 | $ 11,932 | $ 12,035 | $ 12,052 | $ 11,718 | $ 11,117 | $ 10,886 | $ 10,876 | $ 10,889 | $ 11,012 | $ 10,986 | $ 11,197 | $ 11,541 | $ 11,420 | $ 11,835 | $ 12,022 | $ 11,991 | $ 11,537 | $ 11,647 | $ 12,200 | $ 12,466 | ||||||||||||||||||||||||||||||||||||
| C000193180 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | $ 500,000 | $ 506,603 | $ 504,727 | $ 503,846 | $ 509,220 | $ 511,280 | $ 509,237 | $ 519,311 | $ 535,379 | $ 549,963 | $ 547,825 | $ 565,556 | $ 550,299 | $ 565,827 | $ 573,931 | $ 573,157 | $ 584,958 | $ 590,181 | $ 591,142 | $ 574,933 | $ 546,132 | $ 534,486 | $ 534,126 | $ 534,955 | $ 541,143 | $ 540,017 | $ 550,616 | $ 567,699 | $ 562,387 | $ 582,490 | $ 591,890 | $ 590,559 | $ 568,874 | $ 573,980 | $ 601,403 | $ 614,722 | |||||||||||||||||||||||||||||||||||||||||
| Bloomberg Municipal Bond Index | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | $ 10,000 | $ 10,133 | $ 10,314 | $ 9,776 | $ 10,025 | $ 10,281 | $ 10,405 | $ 10,322 | $ 10,276 | $ 10,395 | $ 10,456 | $ 10,439 | $ 10,701 | $ 11,061 | $ 11,368 | $ 11,325 | $ 11,713 | $ 11,501 | $ 11,736 | $ 11,879 | $ 11,837 | $ 12,046 | $ 12,134 | $ 12,114 | $ 11,759 | $ 11,227 | $ 11,087 | $ 11,067 | $ 11,159 | $ 11,282 | $ 11,276 | $ 11,541 | $ 11,764 | $ 11,584 | $ 11,962 | $ 12,110 | $ 12,112 | $ 11,819 | $ 11,971 | $ 12,429 | $ 12,713 | ||||||||||||||||||||||||||||||||||||
| Bloomberg Municipal Bond Index | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Account Value [Line Items] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accumulated Value | $ 500,000 | $ 508,506 | $ 504,440 | $ 502,206 | $ 508,013 | $ 510,989 | $ 510,139 | $ 522,934 | $ 540,548 | $ 555,543 | $ 553,458 | $ 572,410 | $ 562,052 | $ 573,518 | $ 580,547 | $ 578,467 | $ 588,667 | $ 592,995 | $ 591,991 | $ 574,649 | $ 548,673 | $ 541,805 | $ 540,844 | $ 545,356 | $ 551,363 | $ 551,041 | $ 564,005 | $ 574,904 | $ 566,100 | $ 584,591 | $ 591,810 | $ 591,928 | $ 577,579 | $ 585,042 | $ 607,405 | $ 621,305 |