Pension, Profit Sharing and Other Benefit Plans - Fair value by asset category and hierarchy (Details) - Defined Benefit Pension Plans - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	$ 221,311	$ 214,530	$ 209,722
Net Asset Value
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	218,403	195,216
Cash equivalents
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	2,908	19,314
Cash equivalents | Level 1
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	2,908	19,314
Equity securities
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	100,302	107,424
Equity securities | Net Asset Value
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	100,302	107,424
Fixed Income Funds
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	105,651	73,533
Fixed Income Funds | Net Asset Value
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	105,651	73,533
Diversified growth fund
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	8,886	14,259
Diversified growth fund | Net Asset Value
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	8,886	$ 14,259
Real Estate
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	3,564
Real Estate | Net Asset Value
Fair value of assets of defined benefit pension plans by asset category
Fair value of the assets	$ 3,564