Related Party Transactions (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related party transaction, selling, general and administrative expenses from transactions with related party	$ 4,700	$ 7,400	$ 16,500	$ 22,987	$ 19,459	$ 20,852
Payments of ordinary dividends, noncontrolling interest		$ 2,720	1,212	$ 1,212	1,727
Non-controlling Interest
Related party transaction, commission rate		5.00%		5.00%
Royalty Agreements [Member]
Related party transaction, expenses from transactions with related party	$ 2,500	$ 2,300	$ 7,400	$ 9,800	7,400	10,400
Patents and Copyrights [Member]
Related party transaction, expenses from transactions with related party					$ 3,700	$ 10,000

Amount of cash outflow in the form of ordinary dividends provided by the non-wholly owned subsidiary to noncontrolling interests.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585

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- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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- Definition

Identify the stated interest rate per the agreement, for example, leasing and debt arrangements between related parties.

+ References

No definition available.

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- Definition

Amount of selling, general and administrative expenses resulting from transactions, excluding transactions that are eliminated in consolidated or combined financial statements, with related party.

+ References

No definition available.

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