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Employee Benefits - Change in Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
United Kingdom
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 32,423	$ 24,876
Expected return on plan assets	624	586	$ 646
Actual return on plan assets	(584)	979
Employer contributions	153	4,008
Plan participants' contributions	24	22
Benefits paid	(3,049)	(68)
Foreign currency exchange rate changes	(1,670)	2,606
Fair value of plan assets at end of year	27,297	32,423	24,876
Switzerland
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	5,202	6,006
Expected return on plan assets	41	47
Actual return on plan assets	(240)	(296)
Scheme contributions	109	157
Plan participants' contributions	83	120
Transferred (benefits paid)/balances	(77)	(76)
Settlement	(409)	(1,019)
Foreign currency exchange rate changes	(2)	263
Fair value of plan assets at end of year	$ 4,707	$ 5,202	$ 6,006

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Defined Benefit Plan, Scheme Contributions

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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
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Amount of increase (decrease) in plan assets of defined benefit plan from assets transferred into (from) plan.

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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 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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Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

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

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Amount of payment, which decreases plan assets of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract.

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