Schedule of Components of Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6,290	$ 3,730
Interest cost	8,112	6,590
Expected return on assets	(9,104)	(7,698)
Prior service cost (credit)	105	111
Actuarial loss (gain)	3,108	1,202
Termination benefit charge	256
Net periodic benefit cost (credit)	8,767	3,935
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	39	55
Interest cost	230	290
Prior service cost (credit)	(576)	(814)
Actuarial loss (gain)	(82)	(35)
Net periodic benefit cost (credit)	$ (389)	$ (504)

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

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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

-Topic 715

-SubTopic 30

-Glossary Expected Return on Plan Assets

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 60

-Glossary Expected Return on Plan Assets

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (h)(3)

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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

The amount of net gain (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 Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (h)(7)

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Plan Curtailment

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Section 15

-Paragraph 6

-Subparagraph (a)(2)

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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

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (h)(1)

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-Publisher FASB

-Name Accounting Standards Codification

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

-URI http://asc.fasb.org/extlink&oid=6525008

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)(1)

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