Pension Plan and Retirement Benefits - Defined Benefit Plans - Components (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Pension Plans
Components of net periodic pension cost and postretirement health care benefit cost
Service cost	$ 4,080	$ 3,898	$ 3,971
Interest cost	12,050	11,203	11,989
Expected return	(14,380)	(15,117)	(15,033)
Amortization of prior service cost	808	808	808
Recognized actuarial loss	8,838	4,645	4,612
Net periodic cost	11,396	5,437	6,347
Postretirement Health Care Benefits
Components of net periodic pension cost and postretirement health care benefit cost
Service cost	232	337	267
Interest cost	4,595	4,385	4,578
Amortization of prior service cost			(2,895)
Recognized actuarial loss	2,825	2,433	1,996
Net periodic cost	$ 7,652	$ 7,155	$ 3,946