Retirement Plans - Net Periodic Benefit Costs and Benefit Payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 1,278	$ 1,395
Interest cost	22,408	20,933
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2019	43,637
2020	43,835
2021	43,942
2022	43,921
2023	43,691
2025-2029	213,641
Defined Benefit Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	1,278	1,395	$ 1,288
Interest cost	22,376	20,933	22,723
Expected return on assets	(29,654)	(34,267)	(34,056)
Amortization of actuarial loss	10,837	10,744	11,154
Net periodic benefit cost (credit)	$ 4,837	$ (1,195)	$ 1,109