v3.26.1
Pension and Retirement Plans - Components of net periodic benefit costs (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Pension        
Pension and Retirement Plans        
Interest cost $ 116 $ 137 $ 346 $ 350
Expected return on plan assets (114) (156) (341) (400)
Amortization of past service costs 2 2 6 6
Amortization of net gain (1) (2) (2) (5)
Net periodic (benefit) cost 3 (19) 9 (49)
Pension | United Kingdom        
Pension and Retirement Plans        
Interest cost 114 135 341 344
Expected return on plan assets (114) (156) (341) (400)
Amortization of past service costs 2 2 6 6
Amortization of net gain 0 0 0 0
Net periodic (benefit) cost 2 (19) 6 (50)
Pension | U.S.        
Pension and Retirement Plans        
Interest cost 2 2 5 6
Expected return on plan assets 0 0 0 0
Amortization of past service costs 0 0 0 0
Amortization of net gain (1) (2) (2) (5)
Net periodic (benefit) cost 1 0 3 1
Post Retirement:        
Pension and Retirement Plans        
Service cost 6 7 18 20
Interest cost 16 14 47 44
Amortization of net gain (32) (29) (95) (89)
Net periodic (benefit) cost (10) (8) (30) (25)
Post Retirement: | United Kingdom        
Pension and Retirement Plans        
Service cost 0 0 0 0
Interest cost 0 0 0 0
Amortization of net gain 0 0 0 0
Net periodic (benefit) cost 0 0 0 0
Post Retirement: | U.S.        
Pension and Retirement Plans        
Service cost 6 7 18 20
Interest cost 16 14 47 44
Amortization of net gain (32) (29) (95) (89)
Net periodic (benefit) cost $ (10) $ (8) $ (30) $ (25)