Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 1,352	$ 1,346	$ 4,058	$ 4,037
Interest cost	3,356	4,344	10,069	13,031
Expected return on plan assets	(5,647)	(6,100)	(16,943)	(18,300)
Prior service cost (benefit)	0	6	0	19
Net loss (gain)	2,093	941	6,279	2,822
Net periodic benefit cost	1,154	537	3,463	1,609
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer			12,700
Estimated Future Employer Contributions in Current Fiscal Year	0		0
Estimated Future Employer Contributions in Next Fiscal Year	12,700		12,700
Other Postretirement Benefits Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	514	454	1,542	1,362
Interest cost	412	560	1,237	1,683
Expected return on plan assets	(46)	(57)	(137)	(172)
Prior service cost (benefit)	(136)	(99)	(410)	(298)
Net loss (gain)	5	0	15	0
Net periodic benefit cost	749	858	2,247	2,575
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer			4,006
Estimated Future Employer Contributions in Current Fiscal Year	1,335		1,335
Estimated Future Employer Contributions in Next Fiscal Year	5,227		5,227
Supplemental Non-qualified Defined Benefit and Defined Contribution Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	1,035	429	1,482	2,406
Interest cost	274	324	824	972
Prior service cost (benefit)	1	0	1	1
Net loss (gain)	425	134	1,277	402
Net periodic benefit cost	1,735	$ 887	3,584	$ 3,781
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer			1,065
Estimated Future Employer Contributions in Current Fiscal Year	355		355
Estimated Future Employer Contributions in Next Fiscal Year	$ 1,964		$ 1,964