Parent Directory| Name | Size | Last Modified |
|---|---|---|
 0000919574-20-005785-index-headers.html | 2020-09-11 07:27:52 | |
| 0000919574-20-005785-index.html | 2020-09-11 07:27:52 | |
| 0000919574-20-005785.txt | 2020-09-11 07:27:52 | |
 0000919574-20-005785-xbrl.zip | 105414 | 2020-09-11 07:27:52 |
| FilingSummary.xml | 18443 | 2020-09-11 07:27:52 |
| Financial_Report.xlsx | 40848 | 2020-09-11 07:27:52 |
 image0.jpg | 7614 | 2020-09-11 07:27:52 |
| MetaLinks.json | 317425 | 2020-09-11 07:27:52 |
| nat-20200630.htm | 627268 | 2020-09-11 07:27:52 |
| nat-20200630.xsd | 28261 | 2020-09-11 07:27:52 |
| nat-20200630_cal.xml | 53935 | 2020-09-11 07:27:52 |
| nat-20200630_def.xml | 77550 | 2020-09-11 07:27:52 |
| nat-20200630_htm.xml | 288611 | 2020-09-11 07:27:52 |
| nat-20200630_lab.xml | 356505 | 2020-09-11 07:27:52 |
| nat-20200630_pre.xml | 186021 | 2020-09-11 07:27:52 |
| R1.htm | 12389 | 2020-09-11 07:27:52 |
| R10.htm | 19397 | 2020-09-11 07:27:52 |
| R11.htm | 27487 | 2020-09-11 07:27:52 |
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| R19.htm | 17697 | 2020-09-11 07:27:52 |
| R2.htm | 62253 | 2020-09-11 07:27:52 |
| R20.htm | 19745 | 2020-09-11 07:27:52 |
| R21.htm | 11194 | 2020-09-11 07:27:52 |
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| R25.htm | 129055 | 2020-09-11 07:27:52 |
| R26.htm | 11497 | 2020-09-11 07:27:52 |
| R27.htm | 13275 | 2020-09-11 07:27:52 |
| R28.htm | 12025 | 2020-09-11 07:27:52 |
| R29.htm | 33589 | 2020-09-11 07:27:52 |
| R3.htm | 25778 | 2020-09-11 07:27:52 |
| R30.htm | 4344 | 2020-09-11 07:27:52 |
| R31.htm | 16376 | 2020-09-11 07:27:52 |
| R4.htm | 95863 | 2020-09-11 07:27:52 |
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| R6.htm | 85955 | 2020-09-11 07:27:52 |
| R7.htm | 55388 | 2020-09-11 07:27:52 |
| R8.htm | 5838 | 2020-09-11 07:27:52 |
| R9.htm | 6494 | 2020-09-11 07:27:52 |
| report.css | 2767 | 2020-09-11 07:27:52 |
| Show.js | 1085 | 2020-09-11 07:27:52 |