Benefit Plans - Rollforward of Benefit Obligation and Plan Assets Funded (Details) - USD ($) $ in Thousands	12 Months Ended
Aug. 31, 2016	Aug. 31, 2015	Aug. 31, 2014
Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	$ 37,533	$ 36,006	$ 30,417
Interest costs	30,773	28,046	29,900
Expected return on assets	(48,055)	(49,746)	(47,655)
Settlement of retiree obligations	0	0	0
Prior service cost (credit) amortization	1,606	1,631	1,593
Actuarial loss (gain) amortization	19,016	19,621	18,228
Periodic benefit costs, net	$ 40,873	$ 35,558	$ 32,483
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	4.20%	4.00%	4.80%
Expected return on plan assets	6.00%	6.50%	6.75%
Rate of compensation increase	4.90%	4.90%	4.85%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Discount rate	3.60%	4.20%	4.00%
Rate of compensation increase	5.60%	4.90%	4.90%
Non-Qualified Pension Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	$ 1,035	$ 875	$ 860
Interest costs	1,406	1,414	1,660
Expected return on assets	0	0	0
Settlement of retiree obligations	0	1,635	0
Prior service cost (credit) amortization	228	228	229
Actuarial loss (gain) amortization	692	1,058	957
Periodic benefit costs, net	$ 3,361	$ 5,210	$ 3,706
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	4.20%	4.00%	4.50%
Rate of compensation increase	4.90%	5.15%	4.75%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Discount rate	3.30%	4.50%	4.50%
Rate of compensation increase	5.60%	4.80%	4.80%
Other Benefits
Component of net periodic benefit costs: [Abstract]
Service costs	$ 1,412	$ 1,513	$ 1,729
Interest costs	1,709	1,489	1,918
Expected return on assets	0	0	0
Settlement of retiree obligations	0	0	0
Prior service cost (credit) amortization	(120)	(426)	(493)
Actuarial loss (gain) amortization	(464)	(431)	(180)
Periodic benefit costs, net	$ 2,537	$ 2,145	$ 2,974
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	4.20%	4.20%	3.75%
Weighted-average assumptions to determine the net periodic benefit cost: [Abstract]
Discount rate	3.30%	3.75%	4.60%

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

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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 Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Prior Service Cost
-URI http://asc.fasb.org/extlink&oid=49177896

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- Definition

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

+ References

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- Definition

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

+ References

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- Definition

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

+ References

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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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- Definition

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

+ References

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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 Accounting Standards Codification
-Glossary Expected Return on Plan Assets
-URI http://asc.fasb.org/extlink&oid=6512171

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(2)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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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.

+ 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 (h)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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-Publisher FASB
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- Definition

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, but are not limited to, lump-sum cash payments to plan participants in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contracts to cover vested benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 30
-Section 15
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=7577095&loc=d3e8001-114927

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Service Cost (Component of Net Periodic Pension Cost)
-URI http://asc.fasb.org/extlink&oid=6525008

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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