Auction Rate Securities - Significant Assumptions Used to Determine Fair Value of Auction Rate Securities (Details) |
6 Months Ended | 12 Months Ended |
|---|---|---|
Apr. 30, 2018 |
Oct. 31, 2017 |
|
| Schedule of Available-for-sale Securities [Line Items] | ||
| Libor plus stated yield | 2.00% | 2.00% |
| Yields | 2.15% | 2.15% |
| Minimum | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Discount rates | 0.47% | 0.42% |
| Average expected lives | 4 years | 4 years |
| Maximum | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Discount rates | 0.74% | 0.79% |
| Average expected lives | 10 years | 10 years |