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Summary of Significant Accounting Policies - Additional Information (Detail) | 12 Months Ended
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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% |  |

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