v3.26.1
Fair value measurements - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Jun. 30, 2025
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: $ 12,173 $ 12,388 $ 11,634
Total assets measured at fair value $ 91,745 $ 89,636 $ 84,740
Percentage in fixed-income and other investments 52.00% 57.00% 56.00%
Percentage investment in common stock of large-cap companies 20.00% 18.00% 18.00%
Percentage investment in target date investments 11.00% 10.00% 10.00%
Percentage investment in common stock of mid-cap companies 8.00% 7.00% 7.00%
Percentage investment in common stock of small-cap companies 4.00% 4.00% 4.00%
Percentage investment in cash and cash equivalents 3.00% 3.00% 4.00%
Percentage investment in international investments 1.00% 1.00% 1.00%
Percentage investment in real estate 1.00%    
Quoted Prices in Active Markets for Identical Assets (Level 1)      
Debt Securities, Available-for-sale [Line Items]      
Total assets measured at fair value $ 0 $ 0 $ 0
Significant Other Observable Inputs (Level 2)      
Debt Securities, Available-for-sale [Line Items]      
Total assets measured at fair value 91,745 89,636 84,740
Significant Unobservable Inputs (Level 3)      
Debt Securities, Available-for-sale [Line Items]      
Total assets measured at fair value 0 0 0
Mortgage-backed securities      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 8,378 8,363 8,167
Mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 0 0 0
Mortgage-backed securities | Significant Other Observable Inputs (Level 2)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 8,378 8,363 8,167
Mortgage-backed securities | Significant Unobservable Inputs (Level 3)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 0 0 0
U.S. Treasury securities      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 3,795 4,025 3,467
U.S. Treasury securities | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 0 0 0
U.S. Treasury securities | Significant Other Observable Inputs (Level 2)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 3,795 4,025 3,467
U.S. Treasury securities | Significant Unobservable Inputs (Level 3)      
Debt Securities, Available-for-sale [Line Items]      
Available-for-sale securities: 0 0 0
Money market funds      
Debt Securities, Available-for-sale [Line Items]      
Assets: 9,191 9,839 8,965
Money market funds | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Debt Securities, Available-for-sale [Line Items]      
Assets: 0 0 0
Money market funds | Significant Other Observable Inputs (Level 2)      
Debt Securities, Available-for-sale [Line Items]      
Assets: 9,191 9,839 8,965
Money market funds | Significant Unobservable Inputs (Level 3)      
Debt Securities, Available-for-sale [Line Items]      
Assets: 0 0 0
Insurance contracts      
Debt Securities, Available-for-sale [Line Items]      
Assets: 70,381 67,409 64,141
Insurance contracts | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Debt Securities, Available-for-sale [Line Items]      
Assets: 0 0 0
Insurance contracts | Significant Other Observable Inputs (Level 2)      
Debt Securities, Available-for-sale [Line Items]      
Assets: 70,381 67,409 64,141
Insurance contracts | Significant Unobservable Inputs (Level 3)      
Debt Securities, Available-for-sale [Line Items]      
Assets: $ 0 $ 0 $ 0