Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension and Supplemental Executive Retirement Plans
Components of Net Periodic Benefit Cost [Abstract]
Service cost	$ 1,664	$ 1,821
Interest cost	2,810	3,414
Expected return on plan assets	(5,202)	(5,580)
Amortization of net actuarial losses/(gains)	1,550	1,634
Amortization of prior service cost/(credit)	(60)	(62)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	762	1,227
Estimated employer contributions in remainder of fiscal year	6,200
Other Postretirement Benefit Plans
Components of Net Periodic Benefit Cost [Abstract]
Service cost	364	309
Interest cost	164	214
Expected return on plan assets	(2,215)	(1,852)
Amortization of net actuarial losses/(gains)	(439)	(190)
Amortization of prior service cost/(credit)	53	13
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ (2,073)	$ (1,506)