Pension and Postretirement Benefits Postretirement Health and Life Insurance Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			$ 5,621
Additional contributions to the plans are expected during the rest of fiscal 2013			3,058
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	$ 526	$ 510	1,555	$ 1,530
Interest expense	1,462	1,693	4,386	5,080
Amortization of prior service cost	42	48	125	145
Actuarial loss	849	558	2,548	1,672
Net periodic pension cost (benefit)	2,387	1,131	5,013	3,395
Health and Life Insurance Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			475
Additional contributions to the plans are expected during the rest of fiscal 2013			255
Negative plan amendment					$ 4,461
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	0	11	20	32
Interest expense	59	135	280	403
Amortization of prior service cost	(265)	(303)	(271)	(909)
Actuarial loss	99	111	323	333
Net periodic pension cost (benefit)	$ (107)	$ (46)	$ 352	$ (141)