Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 1,346	$ 1,708	$ 4,037	$ 5,125
Interest cost	4,344	3,867	13,031	11,602
Expected return on plan assets	(6,100)	(6,185)	(18,300)	(18,555)
Prior service cost (benefit)	6	15	19	44
Net loss (gain)	941	2,158	2,822	6,473
Net periodic benefit cost	537	1,563	1,609	4,689
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	12,700		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	454	573	1,362	1,718
Interest cost	560	521	1,683	1,563
Expected return on plan assets	(57)	(57)	(172)	(170)
Prior service cost (benefit)	(99)	(99)	(298)	(297)
Net loss (gain)	0	54	0	162
Net periodic benefit cost	858	992	2,575	2,976
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	1,109		3,326
Estimated Future Employer Contributions in Current Fiscal Year	1,109		1,109
Estimated Future Employer Contributions in Next Fiscal Year	4,815		4,815
Supplemental Non-qualified Defined Benefit and Defined Contribution Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	429	632	2,406	1,347
Interest cost	324	293	972	878
Prior service cost (benefit)	0	0	1	1
Net loss (gain)	134	250	402	750
Net periodic benefit cost	887	$ 1,175	3,781	$ 2,976
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	366		1,098
Estimated Future Employer Contributions in Current Fiscal Year	366		366
Estimated Future Employer Contributions in Next Fiscal Year	$ 1,406		$ 1,406