Benefit Plans - Change in Projected Benefit Obligation (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 170,566	$ 161,306
Interest cost	5,542	5,713	$ 6,681
Actuarial (gain) loss	(11,540)	10,148
Benefits paid	(7,204)	(6,601)
Projected benefit obligation at end of year	157,364	170,566	161,306
Change in fair value of plan assets:
Fair value of plan assets at beginning of year	222,124	206,639
Actual (loss) return on plan assets	(5,545)	21,468
Employer contributions	1,133	618
Benefits paid	(7,204)	(6,601)
Fair value of plan assets at end of year	210,508	222,124	$ 206,639
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Asset recognized	53,144	51,558
Accumulated benefit obligation	157,364	170,566
Accrued interest receivable	$ 660	$ 993

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

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Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

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Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

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Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of contribution received by defined benefit plan from employer which increases plan assets.

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of payment to participant under defined benefit plan which decreases plan assets. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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