CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (parenthetical) (USD $)	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Statement of Income and Comprehensive Income [Abstract]
Change in pension and post retirement benefits,tax	$ 13,140,000	$ 7,222,000	$ 493,000

Amount of tax (expense) benefit of other than temporary impairment (OTTI) on investment in available-for-sale debt security, recognized in other comprehensive loss.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 10A

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 35

-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e25362-111560

Name:	us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossTaxIncludingPortionAttributableToNoncontrollingInterestAvailableforsaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration