Net Periodic Benefit Cost (Components of net periodic pension cost and net periodic postretirement benefit cost) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Curtailment/settlement loss		$ 0us-gaap_DefinedBenefitPlanCurtailments
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	2,153	2,481	2,517
Interest cost	9,850	9,716	9,837
Expected return on plan assets	(14,241)	(12,618)	(11,195)
Net amortization	3,517	6,259	6,305
Curtailment/settlement loss	82		0
Net periodic pension cost	1,361	5,838	7,464
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Projected benefit obligation	261,540	225,685
Fair value of plan assets	204,201	188,228
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets [Abstract]
Accumulated benefit obligation	255,295	218,500
Fair value of plan assets	204,201	188,228
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.83%	4.60%	4.35%
Expected long-term rate of return on plan assets	7.50%	7.50%	7.50%
Rate of compensation increase	2.30%	2.00%	2.00%
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost	209	254	285
Net amortization	60	101	81
Net periodic pension cost	$ 269	$ 355	$ 366
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.45%	3.90%

The amount of gains or losses recognized in net periodic benefit cost.

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- Definition

The interest rate used to adjust for the time value of money for the plan.

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- Definition

Expected rate of compensation increases (for pay-related plans).

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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Expected Long-Term Rate of Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512046

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (k)(3)

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- Definition

The amount of decrease that is related to an event that significantly reduces the expected years of future service of present employees or eliminates for a significant number of employees the accrual of defined benefits for some or all of their future services.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)(10)

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Plan Curtailment

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-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Section 15

-Paragraph 6

-Subparagraph (a)(2)

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- Definition

An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Expected Return on Plan Assets

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- Definition

The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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- Definition

The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

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- Definition

If aggregate disclosures are presented, the aggregate pension accumulated benefit obligation for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 55

-Paragraph 17

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- Definition

If aggregate disclosures are presented, the aggregate fair value of plan assets for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

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If aggregate disclosures are presented, the aggregate benefit obligation for plans with benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

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-Publisher FASB

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-SubTopic 20

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-Paragraph 3

-Subparagraph (a)

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- Definition

If aggregate disclosures are presented, the aggregate fair value of plan assets for plans with benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

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- Definition

The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

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-Paragraph 1

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Service Cost (Component of Net Periodic Pension Cost)

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-Publisher FASB

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-Paragraph 1

-Subparagraph (a)(1)

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