Pension and Postretirement Benefits Postretirement Health and Life Insurance Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer	$ 2,127
Additional contributions to the plans are expected during the rest of fiscal 2013	6,552
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	502	$ 510
Interest expense	1,462	1,693
Amortization of prior service cost	42	48
Actuarial loss	849	557
Net periodic pension cost (benefit)	1,301	1,131
Health and Life Insurance Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer	170
Additional contributions to the plans are expected during the rest of fiscal 2013	560
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	10	11
Interest expense	111	134
Amortization of prior service cost	(3)	(303)
Actuarial loss	112	111
Net periodic pension cost (benefit)	$ 230	$ (47)