Employee Benefit Plans (Details 5) (Pension Benefits, USD $) In Thousands, unless otherwise specified								12 Months Ended				12 Months Ended				12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2013 Significant Unobservable Inputs (Level 3)	Mar. 31, 2012 Significant Unobservable Inputs (Level 3)	Mar. 31, 2013 Common/collective trusts	Mar. 31, 2012 Common/collective trusts	Mar. 31, 2013 Common/collective trusts Significant Unobservable Inputs (Level 3)	Mar. 31, 2012 Common/collective trusts Significant Unobservable Inputs (Level 3)	Mar. 31, 2013 Value of funds in insurance company accounts	Mar. 31, 2012 Value of funds in insurance company accounts	Mar. 31, 2013 Value of funds in insurance company accounts Significant Unobservable Inputs (Level 3)	Mar. 31, 2012 Value of funds in insurance company accounts Significant Unobservable Inputs (Level 3)	Mar. 31, 2013 Partnership/joint venture interest	Mar. 31, 2012 Partnership/joint venture interest	Mar. 31, 2013 Partnership/joint venture interest Significant Unobservable Inputs (Level 3)	Mar. 31, 2012 Partnership/joint venture interest Significant Unobservable Inputs (Level 3)
Change in plan assets
Fair value of plan assets at beginning of year	$ 2,357,024	$ 2,154,458	$ 2,063,906	$ 579,363	$ 528,040	$ 518,551	$ 505,551	$ 0	$ 0	$ 45,657	$ 46,026	$ 1,278	$ 1,366	$ 578,403	$ 526,762	$ 526,762	$ 468,796
Realized (losses) gains								0	0			5	(1)			10,229	5,145
Net unrealized gains (losses)								0	0			1	(5)			33,985	9,411
Net purchases, issuances, and settlements								0	0			(79)	(82)			7,182	43,410
Net transfers into (out of) Level 3								0	0			0	0			0	0
Fair value of plan assets at end of year	$ 2,357,024	$ 2,154,458	$ 2,063,906	$ 579,363	$ 528,040	$ 518,551	$ 505,551	$ 0	$ 0	$ 45,657	$ 46,026	$ 1,205	$ 1,278	$ 578,403	$ 526,762	$ 578,158	$ 526,762