Schedule of Change In Plan Assets (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Assets By Fair Value [ Line Items ]
Fair value of plan assets at beginning of year	$ 325,150	$ 311,688
Actual return on plan assets, net	37,308	1,129
Employer contributions	33,400	30,215
Gross benefits paid	(19,415)	(17,882)
Fair value of plan assets at end of year	376,443	325,150
Postretirement Benefit
Defined Benefit Plan Assets By Fair Value [ Line Items ]
Employer contributions	3,994	3,869
Participants' contributions	2,528	1,925
Gross benefits paid	(6,522)	(6,250)
Federal subsidy on benefits paid		$ 456

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.

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+ Details

- Definition

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.

+ References

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-Glossary Postretirement Benefits

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+ Details

- Definition

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.

+ References+ Details