Employee Benefit Plans - Schedule of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2017
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1,780	$ 6,494	$ 7,805	$ 7,621
Interest cost	2,128	8,569	8,489	8,444
Expected return on plan assets	(4,814)	(21,058)	(20,794)	(24,809)
Amortization of Prior service cost	0	0	0	0
Amortization of Net loss	707	3,070	3,117	10,998
Net periodic (income) benefit cost	(199)	(2,925)	(1,383)	2,254
RIM
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	60	210	282	237
Interest cost	111	466	443	429
Expected return on plan assets	0	0	0	0
Amortization of Prior service cost	0	0	0	0
Amortization of Net loss	103	244	413	453
Net periodic (income) benefit cost	274	920	1,138	1,119
Post-retirement
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	92	339	417	471
Interest cost	205	826	796	742
Expected return on plan assets	0	0	0	0
Amortization of Prior service cost	(34)	0	(106)	(136)
Amortization of Net loss	70	147	323	325
Net periodic (income) benefit cost	$ 333	$ 1,312	$ 1,430	$ 1,402