Retirement Plans - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Maximum percent of eligible compensation for 401k plan			6.00%
Company contributions to 401k Plans	$ 4,300,000	$ 2,500,000	$ 11,400,000	$ 9,700,000
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.48%		3.48%
Weighted-average interest crediting rate	2.24%		2.24%
Company contributions to defined benefit plans	$ 0	0	$ 0	0
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Company contributions to defined benefit plans	$ 100,000	$ 100,000	$ 300,000	$ 300,000

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

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Weighted-average interest crediting rate used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, cash balance and other defined benefit plans with promised interest crediting rate.

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

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Amount of discretionary contributions made by an employer to a defined contribution plan.

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Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

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