Summary of Information on Plans' Assets, Projected Benefit Obligations (PBO), and Funded Status (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans
Schedule of Defined Benefit Plan Change in Benefit Obligation [Line Items]
Service Cost	$ 3,006,000	$ 3,573,000	$ 3,227,000
Interest Cost	5,092,000	4,567,000	4,633,000
Employer Contributions	4,191,000	3,700,000	9,387,000
Benefits Paid	(4,246,000)	(3,764,000)	(4,456,000)
PBO at End of Year	121,800,000	96,900,000
Funded Status: Assets vs PBO	(49,918,000)	(25,744,000)
Pension Plans \| Change in Plan Assets
Schedule of Defined Benefit Plan Change in Benefit Obligation [Line Items]
Plan Assets at Beginning of Year	82,551,000	72,411,000
Actual Return on Plan Assets	4,248,000	10,204,000
Employer Contributions	4,191,000	3,700,000
Benefits Paid	(4,246,000)	(3,764,000)
Plan Assets at End of Year	86,744,000	82,551,000
Pension Plans \| Change In Projected Benefit Obligation
Schedule of Defined Benefit Plan Change in Benefit Obligation [Line Items]
PBO at Beginning of Year	108,295,000	116,492,000
Service Cost	3,005,000	3,573,000
Interest Cost	5,092,000	4,567,000
Benefits Paid	(4,246,000)	(3,764,000)
Actuarial (Gain) or Loss	24,516,000	(12,573,000)
PBO at End of Year	136,662,000	108,295,000
Other Postretirement Benefit Plans, Defined Benefit
Schedule of Defined Benefit Plan Change in Benefit Obligation [Line Items]
Service Cost	1,988,000	2,523,000	2,066,000
Interest Cost	2,686,000	2,448,000	2,303,000
Employer Contributions	3,650,000	3,280,000	2,190,000
Participant Contributions	59,000	36,000	18,000
Benefits Paid	(2,184,000)	(1,942,000)	(2,083,000)
Funded Status: Assets vs PBO	(61,083,000)	(46,070,000)
Other Postretirement Benefit Plans, Defined Benefit \| Change in Plan Assets
Schedule of Defined Benefit Plan Change in Benefit Obligation [Line Items]
Plan Assets at Beginning of Year	10,829,000	8,301,000
Actual Return on Plan Assets	486,000	1,154,000
Employer Contributions	3,650,000	3,280,000
Participant Contributions	59,000	36,000
Benefits Paid	(2,184,000)	(1,942,000)
Plan Assets at End of Year	12,840,000	10,829,000
Other Postretirement Benefit Plans, Defined Benefit \| Change In Projected Benefit Obligation
Schedule of Defined Benefit Plan Change in Benefit Obligation [Line Items]
PBO at Beginning of Year	56,899,000	62,092,000
Service Cost	1,988,000	2,523,000
Interest Cost	2,686,000	2,448,000
Participant Contributions	59,000	36,000
Plan Amendments		(183,000)
Benefits Paid	(2,184,000)	(1,942,000)
Actuarial (Gain) or Loss	14,475,000	(8,075,000)
PBO at End of Year	73,923,000	56,899,000
Supplemental Employee Retirement Plans, Defined Benefit
Schedule of Defined Benefit Plan Change in Benefit Obligation [Line Items]
Service Cost	57,000	73,000	289,000
Interest Cost	272,000	241,000	211,000
Employer Contributions	53,000	53,000	53,000
Benefits Paid	(53,000)	(53,000)	(53,000)
PBO at End of Year	6,300,000	5,100,000
Funded Status: Assets vs PBO	(7,965,000)	(5,857,000)
Supplemental Employee Retirement Plans, Defined Benefit \| Change in Plan Assets
Schedule of Defined Benefit Plan Change in Benefit Obligation [Line Items]
Employer Contributions	53,000	53,000
Benefits Paid	(53,000)	(53,000)
Supplemental Employee Retirement Plans, Defined Benefit \| Change In Projected Benefit Obligation
Schedule of Defined Benefit Plan Change in Benefit Obligation [Line Items]
PBO at Beginning of Year	5,857,000	6,207,000
Service Cost	57,000	73,000
Interest Cost	272,000	241,000
Benefits Paid	(53,000)	(53,000)
Actuarial (Gain) or Loss	1,832,000	(611,000)
PBO at End of Year	$ 7,965,000	$ 5,857,000

For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Accumulated Benefit Obligation

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-Publisher FASB

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The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Actual Return on Plan Assets (Component of Net Periodic Postretirement Benefit Cost)

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-Glossary Actual Return on Plan Assets (Component of Net Periodic Pension Cost)

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Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

+ References

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- Definition

1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

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-Glossary Projected Benefit Obligation

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-Name Accounting Standards Codification

-Glossary Accumulated Postretirement Benefit Obligation

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The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.

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The increase in the fair value of plan assets from contributions made by the employer.

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The amount of contributions made by plan participants. This item represents a periodic increase to the plan obligation and an increase to plan assets.

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Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total.

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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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The amount of increase or decrease due to a change in the terms of an existing plan or the initiation of a new plan. A plan amendment may increase or decrease benefits, including those attributed to years of service already rendered.

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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.

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Defined Benefit Plan Fair Value Of Plan Assets Measured On Recurring Basis Unobservable Inputs

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No definition available.

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