v3.26.1
Employee Benefit Plans: (Tables)
 3 Months Ended
Mar. 31, 2026
Retirement Benefits [Abstract]  
Schedule of components of net periodic benefit costs, before allocation to the overhead pool, for Registrant's pension plan, postretirement plan, and SERP
The components of net periodic benefit costs for Registrant’s pension plan, postretirement medical benefit plan and SERP for the three months ended March 31, 2026 and 2025 were as follows:
For The Three Months Ended March 31,
Pension BenefitsOther
Postretirement
Benefits		SERP
(dollars in thousands)202620252026202520262025
Components of Net Periodic Benefits Cost:
Service cost$752 $774 $27 $27 $202 $181 
Interest cost2,713 2,706 19 24 506 485 
Expected return on plan assets(3,554)(3,183)(179)(161)— — 
Amortization of prior service cost109 108 — — — — 
Amortization of actuarial (gain) loss(481)— (71)(291)— — 
Net periodic benefits costs under accounting standards$(461)$405 $(204)$(401)$708 $666