Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension and Supplemental Executive Retirement Plans
Components of Net Periodic Benefit Cost [Abstract]
Service cost	$ 1,848	$ 2,086	$ 5,545	$ 6,258
Interest cost	3,375	3,926	10,125	11,779
Expected return on plan assets	(5,526)	(4,866)	(16,579)	(14,599)
Amortization of net actuarial losses/(gains)	1,580	2,103	4,740	6,309
Amortization of prior service cost/(credit)	(62)	(71)	(186)	(211)
Cost of settlements	6,520	0	6,520	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	7,735	3,178	10,165	9,536
Company contribution to pension plan			12,400
Other Postretirement Benefit Plans
Components of Net Periodic Benefit Cost [Abstract]
Service cost	316	337	947	1,009
Interest cost	208	283	624	848
Expected return on plan assets	(1,852)	(1,447)	(5,556)	(4,339)
Amortization of net actuarial losses/(gains)	(196)	0	(587)	0
Amortization of prior service cost/(credit)	13	(8)	38	(25)
Cost of settlements	0	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ (1,511)	$ (835)	(4,534)	$ (2,507)
Pension Plan
Components of Net Periodic Benefit Cost [Abstract]
Cost of settlements			(6,500)
Company contribution to pension plan			$ 6,500