Employee Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension Benefits [Member]
Components of the Company's net periodic pension and other post-retirement benefit costs
Service cost	$ 557	$ 598	$ 1,113	$ 1,173
Interest cost	7,096	7,386	14,171	14,689
Expected return on plan assets	(7,536)	(7,250)	(15,060)	(14,369)
Amortization of:
Prior service cost	16	15	32	30
Actuarial loss	779	505	1,559	1,004
Net periodic benefit cost	912	1,254	1,815	2,527
Other Post-Retirement Benefits [Member]
Components of the Company's net periodic pension and other post-retirement benefit costs
Service cost	191	176	384	346
Interest cost	247	262	495	521
Amortization of:
Prior service cost	(123)	(122)	(245)	(245)
Actuarial loss	169	161	339	320
Net periodic benefit cost	$ 484	$ 477	$ 973	$ 942