Charge to earnings to fully reserve equity investment and note.

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Maximum term of original maturities to classify as cash equivalent.

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Number of customer accounted for ten percent or more account receivable.

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No definition available.

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Number of customer accounted for ten percent or more sales of net sales.

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Number of financial institutions where Company deposits are maintained.

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Number of largest raw material suppliers.

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No definition available.

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Schedule of significant accounting policies.

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No definition available.

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Valuation allowance for credit losses and disputed amounts.

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No definition available.

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The number of years the Company warrants that its products will be free from material defects in workmanship and materials.

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No definition available.

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Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1
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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount by which inventory stated at last-in first-out (LIFO) is less than (in excess of) inventory stated at other inventory cost methods.

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Amount of consideration paid in advance for advertising that provides economic benefits within a future period of one year or the normal operating cycle, if longer.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) Customer Institution Supplier	Dec. 31, 2017 USD ($) Customer	Dec. 31, 2016 USD ($) Customer
Schedule Of Significant Accounting Policies [Line Items]
Charge to earning to fully reserve the equity investment and note	$ 2,400,000
Maximum term of original maturities to classify as cash equivalent	3 months
Number of financial institutions where deposits are maintained \| Institution	1
Valuation allowance	$ 0	$ 0
Number of customers that accounted for 10% or more of net sales \| Customer	2	2	2
Number of customer accounted for 10% or more account receivable \| Customer	4
Number of largest raw material suppliers \| Supplier	4
Excess of the replacement cost of inventory over the LIFO value of inventory	$ (18,442,000)	$ (20,070,000)
Annual impairment test of goodwill	0	0	$ 0
Goodwill	68,500,000
Impairment loss on contract	0
Valuation allowance	3,015,000	3,096,000
Research and Development costs	4,200,000	3,800,000	3,700,000
Prepaid expenses for production costs of advertising	0	3,800,000	2,400,000
Branding Expenses	$ 35,000,000	$ 31,000,000	$ 24,800,000
Residential Use [Member]
Schedule Of Significant Accounting Policies [Line Items]
Warranty period	25 years
Commercial Use [Member]
Schedule Of Significant Accounting Policies [Line Items]
Warranty period	10 years
Trex Signature Railing [Member] \| Residential Use [Member]
Schedule Of Significant Accounting Policies [Line Items]
Warranty period	25 years
Trex Signature Railing [Member] \| Commercial Use [Member]
Schedule Of Significant Accounting Policies [Line Items]
Warranty period	25 years
Transcend, Enhance, Select and Universal Fascia Product [Member] \| Residential Use [Member]
Schedule Of Significant Accounting Policies [Line Items]
Warranty period	25 years
Transcend, Enhance, Select and Universal Fascia Product [Member] \| Commercial Use [Member]
Schedule Of Significant Accounting Policies [Line Items]
Warranty period	10 years
Commercial Railing and Staging Systems [Member] \| Commercial Use [Member] \| Minimum [Member]
Schedule Of Significant Accounting Policies [Line Items]
Warranty period	1 year
Commercial Railing and Staging Systems [Member] \| Commercial Use [Member] \| Maximum [Member]
Schedule Of Significant Accounting Policies [Line Items]
Warranty period	3 years
Sales Revenue, Net [Member] \| Customer Concentration Risk [Member] \| Minimum [Member]
Schedule Of Significant Accounting Policies [Line Items]
Concentration risk as percentage of total	10.00%	10.00%	10.00%
Sales Revenue, Net [Member] \| Customer Concentration Risk [Member] \| Customer One [Member]
Schedule Of Significant Accounting Policies [Line Items]
Concentration risk as percentage of total	42.00%	41.00%	39.00%
Accounts Receivable [Member] \| Customer Concentration Risk [Member] \| Customer One [Member]
Schedule Of Significant Accounting Policies [Line Items]
Concentration risk as percentage of total	31.00%
Accounts Receivable [Member] \| Customer Concentration Risk [Member] \| Customer Two [Member]
Schedule Of Significant Accounting Policies [Line Items]
Concentration risk as percentage of total	19.00%
Accounts Receivable [Member] \| Customer Concentration Risk [Member] \| Customer Three [Member]
Schedule Of Significant Accounting Policies [Line Items]
Concentration risk as percentage of total	13.00%
Accounts Receivable [Member] \| Customer Concentration Risk [Member] \| Customer Four [Member]
Schedule Of Significant Accounting Policies [Line Items]
Concentration risk as percentage of total	12.00%
Raw Materials [Member] \| Supplier Concentration Risk [Member]
Schedule Of Significant Accounting Policies [Line Items]
Concentration risk as percentage of total	33.00%	33.00%	33.00%
Denplax [Member]
Schedule Of Significant Accounting Policies [Line Items]
Holding company's interest in Denplax	35.00%