Employee Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits [Member]
Components of the Company's net periodic pension and other post-retirement benefit costs
Service cost	$ 603	$ 618	$ 1,776	$ 1,847
Interest cost	7,423	8,182	22,112	24,509
Expected return on plan assets	(7,252)	(7,727)	(21,621)	(23,139)
Amortization of:
Prior service cost	15	21	46	64
Actuarial loss	504	168	1,508	503
Net periodic benefit cost	1,293	1,262	3,821	3,784
Other Post-Retirement Benefits [Member]
Components of the Company's net periodic pension and other post-retirement benefit costs
Service cost	175	126	522	381
Interest cost	262	278	782	837
Amortization of:
Prior service cost	(122)	(122)	(367)	(367)
Actuarial loss	161	123	481	371
Net periodic benefit cost	$ 476	$ 405	$ 1,418	$ 1,222