Retirement Plans - Net Periodic Pension Expense and Narrative (Details) - Defined Benefit Pension Plans - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Net periodic pension expense for defined benefit pension plans
Service cost	$ 4,384	$ 3,981
Interest cost	2,394	4,975
Expected return on assets	(6,356)	(8,279)
Amortization of prior service credit	(218)	(225)
Recognized net actuarial loss	1,402	2,619
Net periodic pension expense	1,606	$ 3,071
Company contributions	7,000
Maximum
Net periodic pension expense for defined benefit pension plans
Expected contributions during next fiscal year	$ 15,000

Amount of gain (loss), recognized immediately as component of net periodic benefit (cost) credit, for change in value of benefit obligation or plan assets from experience different from that assumed, change in actuarial assumption, or consequence of temporarily deviating from substantive plan. Includes, but is not limited to, amount in excess of ten percent of greater of fair value of plan assets or benefit obligation.

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Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

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

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Amount of contributions received and expected to be received by defined benefit plan from employer in current fiscal year.

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Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

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

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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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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