Pensions and Other Postretirement Benefits (Details) (USD $) In Thousands	3 Months Ended	12 Months Ended
Jul. 31, 2011	Jul. 31, 2010	Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2009
Defined Benefit Pension Plans [Member]
Net periodic benefit cost
Service cost	$ 2,062	$ 1,858	$ 7,504	$ 5,755	$ 5,871
Interest cost	6,523	6,346	25,491	24,788	26,263
Expected return on plan assets	(6,885)	(6,657)	(26,848)	(22,894)	(29,905)
Amortization of prior service cost (credit)			1,146	1,362	1,295
Amortization of net actuarial loss (gain)	2,201	1,727	10,294	6,291	1,360
Settlement loss			0	0	9,908
Curtailment	0	3,910	4,095	0	0
Termination benefit cost	0	7,462	8,395	0	0
Other	300	288
Net periodic benefit cost	4,201	14,934	30,077	15,302	14,792
Other Postretirement Benefits [Member]
Net periodic benefit cost
Service cost	525	405	1,620	1,525	1,892
Interest cost	780	690	2,775	2,607	2,540
Expected return on plan assets	0	0	0	0	0
Amortization of prior service cost (credit)			(489)	(489)	(489)
Amortization of net actuarial loss (gain)	(25)	(134)	(536)	(1,043)	(730)
Settlement loss			0	0	0
Curtailment	0	0	0	0	0
Termination benefit cost	0	2,413	2,413	0	0
Other	(100)	(122)
Net periodic benefit cost	$ 1,180	$ 3,252	$ 5,783	$ 2,600	$ 3,213

Other items impacting net periodic benefit costs not separately identified.

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- Definition

The amount of net gain or loss recognized in net periodic benefit cost as a result of special termination benefits offered to and accepted by employees in connection with their termination of employment that are only offered for a short period of time.

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- Definition

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

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph h

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- Definition

The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph h

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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.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 106

-Paragraph 518

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 87

-Paragraph 264

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph h

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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.

+ References

+ Details

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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 or loss, prior service cost or credit, transition asset or obligation, and gain or loss due to settlements or curtailments).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph h

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- Definition

The amount of net gain or loss recognized in net periodic benefit cost as a result of 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 Statement of Financial Accounting Standard (FAS)

-Number 88

-Paragraph 6

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 106

-Paragraph 518

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 87

-Paragraph 264

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph h

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- Definition

The amount of net (gain) loss recognized in net periodic benefit cost as a result of an irrevocable action that relieves the employer (or the plan) of primary responsibility for a benefit obligation and eliminates significant risks related to the obligation and the assets used to effect the settlement. Examples of transactions that constitute a settlement include (a) making lump-sum cash payments to plan participants in exchange for their rights to receive specified benefits and (b) purchasing nonparticipating annuity contracts to cover vested benefits.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 88

-Paragraph 3

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 106

-Paragraph 518

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 87

-Paragraph 264

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph h

+ Details

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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

+ Details

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