Retirement Plans - Schedule of Changes in Fair Value of Plan Assets (Level 3) (Details) - United Kingdom Subsidiary - UK Plan - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 295,968	$ 257,236
Foreign currency exchange rate changes	(15,709)	24,815
Fair value of plan assets at end of year	264,194	295,968
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	103,945	0
Actual return on plan assets, relating to assets still held at reporting date	(71)	1,858
Actual return on plan assets, relating to assets sold during the period	216	0
Purchases, sales and settlements, net	25,523	98,633
Foreign currency exchange rate changes	(7,089)	3,454
Fair value of plan assets at end of year	122,524	103,945
Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	173,575
Fair value of plan assets at end of year	135,780	173,575
Corporate debt securities \| Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	103,945
Fair value of plan assets at end of year	$ 98,077	$ 103,945

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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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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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 of foreign currency translation gain (loss) which increases (decreases) plan assets of defined benefit plan.

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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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