Retirement and Post-Retirement Employee Benefit Plans - Schedule of Employee Pension Plans Investments at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Derivatives, Fair Value [Line Items]
Investments	$ 99,385	$ 88,409
Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	356,883	292,529
Total investments at fair value	529,673	507,640
Common stocks | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	197,577	164,910
Money market funds | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	19,153	9,588
Registered investment companies | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	50,895	64,102
Mortgage-backed securities | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	18,821	15,664
U.S. treasuries | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	23,939	5,951
Corporate bonds | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	46,498	32,314
Common/collective trusts | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments measured at net asset value	108,391	150,976
Limited partnerships | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments measured at net asset value	64,399	64,135
Level 1
Derivatives, Fair Value [Line Items]
Investments	64,151	57,468
Level 1 | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	271,543	234,141
Level 1 | Common stocks | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	197,577	164,910
Level 1 | Money market funds | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 1 | Registered investment companies | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	50,895	64,102
Level 1 | Mortgage-backed securities | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 1 | U.S. treasuries | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	23,071	5,129
Level 1 | Corporate bonds | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 2
Derivatives, Fair Value [Line Items]
Investments	35,234	30,941
Level 2 | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	85,340	58,388
Level 2 | Common stocks | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 2 | Money market funds | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	19,153	9,588
Level 2 | Registered investment companies | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 2 | Mortgage-backed securities | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	18,821	15,664
Level 2 | U.S. treasuries | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	868	822
Level 2 | Corporate bonds | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	46,498	32,314
Level 3
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 3 | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 3 | Common stocks | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 3 | Money market funds | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 3 | Registered investment companies | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 3 | Mortgage-backed securities | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 3 | U.S. treasuries | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	0	0
Level 3 | Corporate bonds | Defined Benefit Plan
Derivatives, Fair Value [Line Items]
Investments	$ 0	$ 0