Financial instruments - aggregate accounts receivable, net of allowance for doubtful accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Derivatives Fair Value [Line Items]
Allowance for doubtful accounts	$ 9,348	$ 10,255
Current portion of allowance for doubtful accounts	4,400	3,500
Concentration Countries Greece, Italy, Spain And Portugal [Member]
Derivatives Fair Value [Line Items]
Accounts receivable, net	$ 39,026	$ 49,054
Entity wide by country, percentage	11.00%	14.60%
Spain, Italy, Portugal, and Greece
Derivatives Fair Value [Line Items]
Long-term portion of trade accounts receivable, net from customers	$ 2,700	$ 3,300
Italy
Derivatives Fair Value [Line Items]
Receivables sold	12,700
Portugal
Derivatives Fair Value [Line Items]
Receivables sold	$ 12,600

Accounts Receivable, Entity Wide By Country, Percentage

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For an unclassified balance sheet, the amount due from customers or clients for goods or services that have been delivered or sold in the normal course of business, reduced to their estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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- Definition

Amount due from customers or clients, more than one year from the balance sheet date, for goods or services that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

+ References

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For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible.

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A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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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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The amount of any significant sales of financing receivables during the reporting period.

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