Pension and Postretirement Benefits - Amounts Recognized in Consolidated Statements of Financial Position (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of benefit obligation
Service cost	$ 523	$ 499	$ 63
Interest cost on projected benefit obligation	17,421	15,846	18,772
Reconciliation of fair value of plan assets
Fair value of plan assets at January 1,	402,579
Fair value of plan assets at December 31,	470,101	402,579
Qualified
Reconciliation of benefit obligation
Obligation at January 1,	344,974	415,824
Service cost	524	498
Interest cost on projected benefit obligation	14,867	13,428
Actuarial (gain) loss	48,210	(57,807)
Benefits paid	(21,302)	(26,969)
Obligation at December 31,	387,273	344,974	415,824
Reconciliation of fair value of plan assets
Fair value of plan assets at January 1,	402,579	382,724
Actual return on plan assets	88,827	(13,184)
Employer contributions	0	60,000
Benefits paid	(21,305)	(26,961)
Fair value of plan assets at December 31,	470,101	402,579	382,724
Funded status
Funded status at December 31,	82,828	57,605
Non-qualified
Reconciliation of benefit obligation
Obligation at January 1,	68,035	75,014
Service cost	0	0
Interest cost on projected benefit obligation	2,554	2,418
Actuarial (gain) loss	3,847	(496)
Benefits paid	(8,703)	(8,901)
Obligation at December 31,	65,733	68,035	75,014
Reconciliation of fair value of plan assets
Fair value of plan assets at January 1,	0	0
Actual return on plan assets	0	0
Employer contributions	8,703	8,901
Benefits paid	(8,703)	(8,901)
Fair value of plan assets at December 31,	0	0	$ 0
Funded status
Funded status at December 31,	$ (65,733)	$ (68,035)

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

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