Mid Cap Index Fund Investment Strategy - Mid Cap Index Fund	May 31, 2026
Prospectus [Line Items]
Strategy [Heading]	<span style="color:#000000;font-family:Arial;font-size:12pt;font-weight:bold;">Principal Investment Strategies of the Fund</span>
Strategy Narrative [Text Block]	The Fund is managed to seek to track the performance of the Index, which measures the performance of the mid-capitalization sector of the U.S. equity market.The Subadviser may endeavor to track the Index by purchasing every stock included in the Index, in the same proportions; or, in the alternative, the Subadviser may invest in a sampling of Index stocks by utilizing a statistical technique known as “optimization.” The goal of optimization is to select stocks which ensure that various industry weightings, market capitalizations, and fundamental characteristics, (e.g., price-to-book, price-to-earnings, debt-to-asset ratios and dividend yields) closely approximate those of the Index.Under normal circumstances, at least 80% of the Fund’s net assets are invested in stocks that are in the Index.Although the Fund seeks to track the performance of the Index, the performance of the Fund will not match that of the Index exactly because, among other reasons, the Fund incurs operating expenses and other investment overhead as part of its normal operations. The subadviser may use derivatives to seek to track the performance of the Index, including futures and total return swaps. In order to generate additional income, the Fund may lend portfolio securities to broker-dealers and other financial institutions provided that the value of the loaned securities does not exceed 30% of the Fund’s total assets. These loans earn income for the Fund and are collateralized by cash and securities issued or guaranteed by the U.S. Government or its agencies or instrumentalities.

Mid Cap Index Fund Investment Strategy - Mid Cap Index Fund

May 31, 2026

<span style="color:#000000;font-family:Arial;font-size:12pt;font-weight:bold;">Principal Investment Strategies of the Fund</span>

Strategy Narrative [Text Block]

The Fund is managed to seek to track the performance of the Index, which measures the performance of the mid-capitalization sector of the U.S. equity market.The Subadviser may endeavor to track the Index by purchasing every stock included in the Index, in the same proportions; or, in the alternative, the Subadviser may invest in a sampling of Index stocks by utilizing a statistical technique known as “optimization.” The goal of optimization is to select stocks which ensure that various industry weightings, market capitalizations, and fundamental characteristics, (e.g., price-to-book, price-to-earnings, debt-to-asset ratios and dividend yields) closely approximate those of the Index.Under normal circumstances, at least 80% of the Fund’s net assets are invested in stocks that are in the Index.Although the Fund seeks to track the performance of the Index, the performance of the Fund will not match that of the Index exactly because, among other reasons, the Fund incurs operating expenses and other investment overhead as part of its normal operations. The subadviser may use derivatives to seek to track the performance of the Index, including futures and total return swaps. In order to generate additional income, the Fund may lend portfolio securities to broker-dealers and other financial institutions provided that the value of the loaned securities does not exceed 30% of the Fund’s total assets. These loans earn income for the Fund and are collateralized by cash and securities issued or guaranteed by the U.S. Government or its agencies or instrumentalities.