Retirement and Post-Retirement Employee Benefit Plans - Schedule of Net Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Supplemental Executive Retirement Plans
Components of net periodic postretirement cost:
Service cost	$ 1,332	$ 2,756	$ 2,371
Interest cost	4,988	4,744	5,185
Recognized actuarial loss	3,079	4,251	2,586
Settlements	4,159	2,685	0
Net periodic pension cost	13,558	14,436	10,142
Defined Benefit Plan
Components of net periodic postretirement cost:
Service cost	17,264	18,109	16,419
Interest cost	20,803	20,443	23,193
Expected return on assets	(27,666)	(27,975)	(27,522)
Amortization of prior service cost	(231)	(231)	(226)
Recognized actuarial loss	9,114	12,744	10,693
Net periodic pension cost	$ 19,284	$ 23,090	$ 22,557