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, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1,780	$ 7,805	$ 7,496	$ 7,621	$ 6,188
Interest cost	2,128	8,489	8,461	8,444	8,096
Expected return on plan assets	(4,814)	(20,794)		(24,809)	(22,706)
Amortization of Prior service cost	0	0		0	0
Amortization of Net loss	707	3,117		10,998	8,490
Net periodic (income) cost	(199)	(1,383)		2,254	68
RIM
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	60	282	238	237	140
Interest cost	111	443	433	429	385
Expected return on plan assets	0	0		0	0
Amortization of Prior service cost	0	0		0	0
Amortization of Net loss	103	413		453	283
Net periodic (income) cost	274	1,138		1,119	808
Post-retirement
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	92	417	445	471	447
Interest cost	205	796	$ 762	742	854
Expected return on plan assets	0	0		0	0
Amortization of Prior service cost	(34)	(106)		(136)	(136)
Amortization of Net loss	70	323		325	339
Net periodic (income) cost	$ 333	$ 1,430		$ 1,402	$ 1,504