Employee Benefit Plans and Postretirement Health Care and Life Insurance Benefits (Plans' Expenses and Expected Future Benefit Payments) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Pension Benefits
Components of the Company's net periodic pension and other post-retirement benefit costs
Service cost	$ 2,384	$ 2,231	$ 3,168
Interest cost	29,711	33,076	33,357
Expected return on plan assets	(29,012)	(31,214)	(28,862)
Amortization of:
Prior service cost	62	88	221
Actuarial loss	2,019	665	1,037
Net periodic benefit cost	5,164	4,846	8,921
Expected future benefit payments
2014	40,931
2015	37,012
2016	37,893
2017	38,467
2018	40,125
2019 to 2023	207,940
Other Post-Retirement Benefits
Components of the Company's net periodic pension and other post-retirement benefit costs
Service cost	700	516	185
Interest cost	1,046	1,123	1,020
Amortization of:
Prior service cost	(490)	(490)	(490)
Actuarial loss	642	498	110
Net periodic benefit cost	1,898	1,647	825
Expected future benefit payments
2014	1,894
2015	1,815
2016	1,777
2017	1,767
2018	1,725
2019 to 2023	$ 7,826