Postretirement Benefit Plans - Obligations and Funded Status (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
United States [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation at beginning of year	$ 160,789	$ 169,407
Interest cost	6,934	6,815	$ 6,936
Actuarial (gain) loss	1,538	(9,315)
Benefits paid	(6,534)	(6,118)
Benefit obligation at end of year	162,727	160,789	169,407
Fair value of plan assets at beginning of year	121,835	126,369
Actual return on plan assets	21,612	1,374
Employer contributions	179	210
Fair value of plan assets at end of year	137,092	121,835	126,369
Over (Under) funded status at end of year	(25,635)	(38,954)
United Kingdom [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation at beginning of year	19,950	22,983
Interest cost	733	789	964
Actuarial (gain) loss	5,614	(1,763)
Benefits paid	(513)	(891)
Foreign exchange impact	(3,750)	(1,168)
Benefit obligation at end of year	22,034	19,950	22,983
Fair value of plan assets at beginning of year	21,425	22,858
Actual return on plan assets	2,758	72
Employer contributions	378	605
Foreign exchange impact	(3,712)	(1,219)
Fair value of plan assets at end of year	20,336	21,425	$ 22,858
Over (Under) funded status at end of year	$ (1,698)	$ 1,475

Pension plans postretirement and other employee benefits.

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- Definition

The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Actual Return on Plan Assets (Component of Net Periodic Postretirement Benefit Cost)
-URI http://asc.fasb.org/extlink&oid=6504192

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
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-Publisher FASB
-Name Accounting Standards Codification
-Glossary Actual Return on Plan Assets (Component of Net Periodic Pension Cost)
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- Definition

Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Gain or Loss
-URI http://asc.fasb.org/extlink&oid=49168827

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- Definition

1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

+ References

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- Definition

The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.

+ References

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-Topic 715
-SubTopic 60
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount of contributions made by the employer to defined benefit plans.

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- Definition

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.

+ References

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-Publisher FASB
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- Definition

Amount of gain (loss) from foreign currency exchange rate changes for benefit obligation for plans of a foreign operation whose functional currency is not the reporting currency.

+ References

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The amount of increase or decrease in plan assets attributed to foreign currency changes. The effects of foreign currency exchange rate changes that are to be disclosed are those applicable to plans of a foreign operation whose functional currency is not the reporting currency.

+ References

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- Definition

The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total.

+ References

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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