Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension and Supplemental Executive Retirement Plans
Components of Net Periodic Benefit Cost [Abstract]
Service cost	$ 1,908	$ 1,848	$ 5,724	$ 5,545
Interest cost	2,794	3,375	8,383	10,125
Expected return on plan assets	(5,229)	(5,526)	(15,687)	(16,579)
Amortization of net actuarial losses (gains)	1,403	1,580	4,208	4,740
Amortization of prior service cost (credit)	(60)	(62)	(179)	(186)
Cost of settlements	4,732	6,520	4,732	6,520
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	5,548	7,735	7,181	10,165
Company contribution to pension and supplemental executive retirement plans			6,900
Other Postretirement Benefit Plans
Components of Net Periodic Benefit Cost [Abstract]
Service cost	377	316	1,131	947
Interest cost	163	208	487	624
Expected return on plan assets	(2,216)	(1,852)	(6,647)	(5,556)
Amortization of net actuarial losses (gains)	(425)	(196)	(1,273)	(587)
Amortization of prior service cost (credit)	53	13	159	38
Cost of settlements	0	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ (2,048)	$ (1,511)	(6,143)	(4,534)
Pension Plan
Components of Net Periodic Benefit Cost [Abstract]
Cost of settlements			$ 4,700	$ 6,500