Parent Directory| Name | Size | Last Modified |
|---|---|---|
 0001064728-22-000042-index-headers.html | 2022-05-05 06:38:49 | |
| 0001064728-22-000042-index.html | 2022-05-05 06:38:49 | |
| 0001064728-22-000042.txt | 2022-05-05 06:38:49 | |
 0001064728-22-000042-xbrl.zip | 516411 | 2022-05-05 06:38:49 |
| btu-20220331.htm | 2011978 | 2022-05-05 06:38:49 |
| btu-20220331.xsd | 67864 | 2022-05-05 06:38:49 |
| btu-20220331_cal.xml | 96854 | 2022-05-05 06:38:49 |
| btu-20220331_def.xml | 397163 | 2022-05-05 06:38:49 |
 btu-20220331_g1.jpg | 195073 | 2022-05-05 06:38:49 |
| btu-20220331_htm.xml | 1633093 | 2022-05-05 06:38:49 |
| btu-20220331_lab.xml | 773053 | 2022-05-05 06:38:49 |
| btu-20220331_pre.xml | 572101 | 2022-05-05 06:38:49 |
| btu_20220331xex104.htm | 496990 | 2022-05-05 06:38:49 |
| btu_20220331xex311.htm | 10817 | 2022-05-05 06:38:49 |
| btu_20220331xex312.htm | 10857 | 2022-05-05 06:38:49 |
| btu_20220331xex321.htm | 5752 | 2022-05-05 06:38:49 |
| btu_20220331xex322.htm | 5783 | 2022-05-05 06:38:49 |
| btu_20220331xex95.htm | 112240 | 2022-05-05 06:38:49 |
| FilingSummary.xml | 43750 | 2022-05-05 06:38:49 |
| Financial_Report.xlsx | 108654 | 2022-05-05 06:38:49 |
 image_0a.jpg | 12115 | 2022-05-05 06:38:49 |
| MetaLinks.json | 826440 | 2022-05-05 06:38:49 |
| R1.htm | 54576 | 2022-05-05 06:38:49 |
| R10.htm | 6994 | 2022-05-05 06:38:49 |
| R11.htm | 19896 | 2022-05-05 06:38:49 |
| R12.htm | 73051 | 2022-05-05 06:38:49 |
| R13.htm | 21064 | 2022-05-05 06:38:49 |
| R14.htm | 11378 | 2022-05-05 06:38:49 |
| R15.htm | 8767 | 2022-05-05 06:38:49 |
| R16.htm | 102321 | 2022-05-05 06:38:49 |
| R17.htm | 14141 | 2022-05-05 06:38:49 |
| R18.htm | 130950 | 2022-05-05 06:38:49 |
| R19.htm | 7422 | 2022-05-05 06:38:49 |
| R2.htm | 122979 | 2022-05-05 06:38:49 |
| R20.htm | 44135 | 2022-05-05 06:38:49 |
| R21.htm | 26965 | 2022-05-05 06:38:49 |
| R22.htm | 17631 | 2022-05-05 06:38:49 |
| R23.htm | 30576 | 2022-05-05 06:38:49 |
| R24.htm | 13609 | 2022-05-05 06:38:49 |
| R25.htm | 16228 | 2022-05-05 06:38:49 |
| R26.htm | 51620 | 2022-05-05 06:38:49 |
| R27.htm | 11202 | 2022-05-05 06:38:49 |
| R28.htm | 71868 | 2022-05-05 06:38:49 |
| R29.htm | 18898 | 2022-05-05 06:38:49 |
| R3.htm | 34437 | 2022-05-05 06:38:49 |
| R30.htm | 11960 | 2022-05-05 06:38:49 |
| R31.htm | 91733 | 2022-05-05 06:38:49 |
| R32.htm | 12765 | 2022-05-05 06:38:49 |
| R33.htm | 84823 | 2022-05-05 06:38:49 |
| R34.htm | 23270 | 2022-05-05 06:38:49 |
| R35.htm | 22367 | 2022-05-05 06:38:49 |
| R36.htm | 16458 | 2022-05-05 06:38:49 |
| R37.htm | 26370 | 2022-05-05 06:38:49 |
| R38.htm | 48870 | 2022-05-05 06:38:49 |
| R39.htm | 7418 | 2022-05-05 06:38:49 |
| R4.htm | 5326 | 2022-05-05 06:38:49 |
| R40.htm | 65730 | 2022-05-05 06:38:49 |
| R41.htm | 10328 | 2022-05-05 06:38:49 |
| R42.htm | 52482 | 2022-05-05 06:38:49 |
| R43.htm | 21605 | 2022-05-05 06:38:49 |
| R44.htm | 20028 | 2022-05-05 06:38:49 |
| R45.htm | 15760 | 2022-05-05 06:38:49 |
| R46.htm | 22327 | 2022-05-05 06:38:49 |
| R47.htm | 84528 | 2022-05-05 06:38:49 |
| R48.htm | 37694 | 2022-05-05 06:38:49 |
| R49.htm | 19645 | 2022-05-05 06:38:49 |
| R5.htm | 144654 | 2022-05-05 06:38:49 |
| R50.htm | 30885 | 2022-05-05 06:38:49 |
| R51.htm | 15777 | 2022-05-05 06:38:49 |
| R52.htm | 17238 | 2022-05-05 06:38:49 |
| R53.htm | 6063 | 2022-05-05 06:38:49 |
| R54.htm | 9314 | 2022-05-05 06:38:49 |
| R55.htm | 20571 | 2022-05-05 06:38:49 |
| R56.htm | 36296 | 2022-05-05 06:38:49 |
| R57.htm | 14577 | 2022-05-05 06:38:49 |
| R58.htm | 41051 | 2022-05-05 06:38:49 |
| R59.htm | 8718 | 2022-05-05 06:38:49 |
| R6.htm | 32301 | 2022-05-05 06:38:49 |
| R60.htm | 33582 | 2022-05-05 06:38:49 |
| R61.htm | 171616 | 2022-05-05 06:38:49 |
| R62.htm | 23367 | 2022-05-05 06:38:49 |
| R63.htm | 8497 | 2022-05-05 06:38:49 |
| R64.htm | 32107 | 2022-05-05 06:38:49 |
| R65.htm | 5526 | 2022-05-05 06:38:49 |
| R66.htm | 10017 | 2022-05-05 06:38:49 |
| R67.htm | 54521 | 2022-05-05 06:38:49 |
| R68.htm | 65498 | 2022-05-05 06:38:49 |
| R69.htm | 8133 | 2022-05-05 06:38:49 |
| R7.htm | 117635 | 2022-05-05 06:38:49 |
| R70.htm | 25125 | 2022-05-05 06:38:49 |
| R71.htm | 39912 | 2022-05-05 06:38:49 |
| R8.htm | 51176 | 2022-05-05 06:38:49 |
| R9.htm | 5669 | 2022-05-05 06:38:49 |
| report.css | 2767 | 2022-05-05 06:38:49 |
| Show.js | 1085 | 2022-05-05 06:38:49 |