Employee Benefits - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Percentage of matching contribution if compensation percentage below low range	100.00%
Matching participant's contribution, percentage on compensation	4.00%
Percentage of matching contribution if compensation percentage between high range and low range	75.00%
Matching participant's contribution, percentage on compensation, range low	4.00%
Matching participant's contribution, percentage on compensation, range high	8.00%
Percentage of employees eligible to accrue benefits under the defined plan	50.00%
Matching participant's contribution, average percentage on compensation	6.00%
Retirement liabilities	$ 228,936,000	$ 243,407,000
Capital in excess of par value related to Deferred Compensation Plan	22,500,000	18,800,000
Total cash surrender value of life insurance contracts	45,216,000	43,425,000
Pension cost (reversal of cost)	(8,000,000)
1% increase in accumulated postretirement benefit obligation	300,000
1% increase in postretirement expense	100,000
1% decrease in accumulated postretirement benefit obligation	400,000
1% decrease in postretirement expense	100,000
Deferred Compensation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Retirement liabilities	43,000,000	37,600,000
U.K. Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension cost (reversal of cost)	2,800,000
Pension Plan [Member] \| U.S Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Retirement liabilities	49,981,000	51,684,000
Contribution to the plans	5,123,000	$ 23,519,000
Pension Plan [Member] \| U.S Plans [Member] \| Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target percentage of investment in equity securities		20.00%
Pension Plan [Member] \| U.S Plans [Member] \| Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target percentage of investment in equity securities		80.00%
Pension Plan [Member] \| U.S Plans [Member] \| Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution to the plans	0
Pension Plan [Member] \| U.S Plans [Member] \| Nonqualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution to the plans	3,500,000
Pension Plan [Member] \| Non-U.S. Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Retirement liabilities	80,694,000	$ 102,871,000
Contribution to the plans	$ 36,645,000	$ 23,239,000
Pension Plan [Member] \| Non-U.S. Plans [Member] \| Alternative and other investments [Member] \| Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target percentage of investment in equity securities	5.00%
Pension Plan [Member] \| Non-U.S. Plans [Member] \| Alternative and other investments [Member] \| Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target percentage of investment in equity securities	10.00%
Pension Plan [Member] \| Non-U.S. Plans [Member] \| Real Estate [Member] \| Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target percentage of investment in equity securities	5.00%
Pension Plan [Member] \| Non-U.S. Plans [Member] \| Real Estate [Member] \| Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target percentage of investment in equity securities	20.00%
Pension Plan [Member] \| Non-U.S. Plans [Member] \| Equity Securities [Member] \| Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target percentage of investment in equity securities	15.00%
Pension Plan [Member] \| Non-U.S. Plans [Member] \| Equity Securities [Member] \| Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target percentage of investment in equity securities	40.00%
Pension Plan [Member] \| Non-U.S. Plans [Member] \| Fixed Income Securities [Member] \| Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target percentage of investment in equity securities	40.00%
Pension Plan [Member] \| Non-U.S. Plans [Member] \| Fixed Income Securities [Member] \| Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target percentage of investment in equity securities	70.00%
Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution to the plans	$ 3,900,000

Portion of Deferred Compensation Plan to be paid out in shares.

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Defined contribution plan, matching participant contribution, average percentage on compensation

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Defined contribution plan, matching participant contribution, percentage on compensation, range high

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Carrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity.

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

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Amount of decrease in accumulated postretirement benefit obligation from one-percentage-point decrease in assumed health care cost trend rate.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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