v3.26.1
Average Annual Total Returns - Third Avenue Value Portfolio
 12 Months Ended 60 Months Ended 120 Months Ended 315 Months Ended
Apr. 24, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Prospectus [Line Items]          
Average Annual Return, Percent   34.85% 17.68% 9.66% 8.67%
Performance Inception Date Sep. 21, 1999        
MSCI World Index (reflects no deductions for fees, expenses or taxes)          
Prospectus [Line Items]          
Average Annual Return, Percent [1]   21.60% 12.66% 12.74% 7.41%
Performance Inception Date Sep. 21, 1999        
[1] An index is a hypothetical measure of performance based on the ups and downs in the values of securities representative of a particular market. The MSCI World Index is captures large and mid-cap representation across 23 Developed Markets countries. With 1,320 constituents, the MSCI World Index covers approximately 85% of the free float-adjusted market capitalization in each country. The MSCI World Index is not a security that can be purchased or sold, and its total returns are reflective of unmanaged portfolios. It is not possible to invest directly in an unmanaged index.