v3.26.1
Retirement Benefits - Net Periodic Benefit Cost (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2026
Qualified Pension Benefits          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Service cost $ 4,419 $ 4,206 $ 8,839 $ 8,412  
Interest cost 8,024 8,054 16,047 16,107  
Expected return on plan assets (14,314) (14,061) (28,628) (28,122)  
Amortization of prior service cost 0 0 0 0  
Amortization of net loss (gain) (609) (1,196) (1,217) (2,391)  
Net periodic benefit cost (2,480) (2,997) (4,959) (5,994)  
Qualified Pension Benefits | Forecast          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Aggregate expected contributions         $ 18,000
Qualified Pension Benefits | Subsidiaries          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Service cost 4,419 4,206 8,839 8,412  
Interest cost 8,024 8,054 16,047 16,107  
Expected return on plan assets (14,314) (14,061) (28,628) (28,122)  
Amortization of prior service cost 0 0 0 0  
Amortization of net loss (gain) 0 0 0 0  
Net periodic benefit cost (1,871) (1,801) (3,742) (3,603)  
SERP Pension Benefits          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Service cost 0 0 0 0  
Interest cost 280 307 559 613  
Expected return on plan assets 0 0 0 0  
Amortization of prior service cost 0 0 0 0  
Amortization of net loss (gain) (42) (50) (83) (99)  
Net periodic benefit cost 238 257 476 514  
Employer contributions     2,000 3,000  
SERP Pension Benefits | Forecast          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Aggregate expected contributions         3,400
SERP Pension Benefits | Subsidiaries          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Service cost 0 0 0 0  
Interest cost 279 306 559 613  
Expected return on plan assets 0 0 0 0  
Amortization of prior service cost 0 0 0 0  
Amortization of net loss (gain) (37) (45) (74) (89)  
Net periodic benefit cost 242 261 485 524  
Other Benefits          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Service cost 44 51 89 102  
Interest cost 102 108 204 217  
Expected return on plan assets (73) (73) (146) (146)  
Amortization of prior service cost 9 9 17 17  
Amortization of net loss (gain) (59) (46) (119) (91)  
Net periodic benefit cost 23 49 45 99  
Other Benefits | Forecast          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Aggregate expected contributions         $ 200
Other Benefits | Subsidiaries          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Service cost 44 51 89 102  
Interest cost 102 108 204 217  
Expected return on plan assets (73) (72) (146) (145)  
Amortization of prior service cost 9 9 17 17  
Amortization of net loss (gain) (60) (47) (121) (94)  
Net periodic benefit cost $ 22 $ 49 $ 43 $ 97