Pension, Profit Sharing and Other Benefit Plans - Fair value by asset category and hierarchy (Details) - Defined Benefit Pension Plans - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	$ 214,530	$ 209,722	$ 194,253
Net Asset Value
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	195,216	207,057
Cash and cash equivalents
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	19,314	2,665
Cash and cash equivalents | Level 1
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	19,314	2,665
Equity securities
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	107,424	101,433
Equity securities | Net Asset Value
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	107,424	101,433
Fixed-income funds
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	73,533	84,188
Fixed-income funds | Net Asset Value
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	73,533	84,188
Diversified growth fund
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	14,259	16,646
Diversified growth fund | Net Asset Value
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	$ 14,259	16,646
Real Estate
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets		4,790
Real Estate | Net Asset Value
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets		$ 4,790