Pension and Postretirement Benefits Postretirement Health and Life Insurance Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer	$ 1,503
Additional contributions to the plans are expected during the rest of current fiscal year	4,957
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	120	$ 502
Interest expense	1,176	1,462
Amortization of prior service cost	10	42
Actuarial loss	524	849
Net periodic pension cost	427	1,301
Health and Life Insurance Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer	83
Additional contributions to the plans are expected during the rest of current fiscal year	291
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	3	10
Interest expense	67	111
Amortization of prior service cost	(177)	(3)
Actuarial loss	104	112
Net periodic pension cost	$ (3)	$ 230