Mid-Cap Index Portfolio Average Annual Total Returns - Portfolio [Member] |
12 Months Ended | 60 Months Ended | 120 Months Ended |
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2025 |
Dec. 31, 2025 |
|
| CRSP US Mid Cap Index (reflects no deduction for fees, expenses, or taxes)[Member] | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 11.70% | 8.62% | 10.94% |
| Dow Jones U.S. Total Stock Market Float Adjusted Index (reflects no deduction for fees, expenses, or taxes)[Member] | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 17.05% | 13.07% | 14.21% |
| Mid-Cap Index Portfolio | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 11.54% | 8.46% | 10.77% |