Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Qualified Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 11,028	$ 10,290	$ 41,897	$ 36,015
Interest cost	11,251	10,108	41,575	44,275
Expected return on plan assets	(19,978)	(18,088)	(74,242)	(67,060)
Amortization of net actuarial loss	8,117	10,489	39,583	37,507
Net periodic benefit cost	10,418	12,799	48,813	50,737
SERP
Defined Benefit Plan Disclosure [Line Items]
Service cost	106	131	501	422
Interest cost	360	358	1,433	1,561
Amortization of net actuarial loss	588	660	2,570	2,014
Net periodic benefit cost	1,054	1,149	4,504	3,997
PBOP
Defined Benefit Plan Disclosure [Line Items]
Service cost	485	423	1,753	1,608
Interest cost	613	548	2,258	2,485
Expected return on plan assets	(807)	(810)	(3,236)	(3,366)
Amortization of prior service costs	44	240	763	1,106
Net periodic benefit cost	$ 335	$ 401	$ 1,538	$ 1,833