Employee Benefit Plans - Changes in Pension Plan Level 3 Assets (Details) - Pension Plans - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Summary of changes in fair value of the pension plans' level 3 assets
Fair value of plan assets at January 1	$ 1,941,330	$ 1,787,075
Return on plan assets:
Fair value of plan assets at December 31	1,725,543	1,941,330
Level 3
Summary of changes in fair value of the pension plans' level 3 assets
Fair value of plan assets at January 1	114,593	102,884
Return on plan assets:
Relating to assets still held at the reporting date	6,762	10,795
Relating to assets sold during the period	(38)	(405)
Purchases, sales, settlements and expenses	519	1,319
Fair value of plan assets at December 31	$ 121,836	$ 114,593

No definition available.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

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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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- Definition

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.

+ References

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- Definition

Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment.

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