```ts
export function postingLists(documents: string[]): Record<string, number[]> {
  if (!Array.isArray(documents)) {
    throw new Error('Input must be an array of strings');
  }

  const index: Record<string, number[]> = {};

  documents.forEach((doc, docIndex) => {
    if (typeof doc !== 'string') {
      throw new Error('All documents must be strings');
    }

    const terms = doc.match(/[a-z\d]+/gi);
    if (!terms) return;

    terms.forEach(term => {
      term = term.toLowerCase();
      if (term.length <= 1 || /^\d+$/.test(term)) return;

      if (!index[term]) index[term] = [];
      if (!index[term].includes(docIndex)) index[term].push(docIndex);
    });
  });

  return index;
}
```