Commitments and Contingencies - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Sep. 30, 2013 Letter	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Commitments And Contingencies [Line Items]
Payments related to mold growth litigation		$ 1,800,000
Maximum expected total payments under the settlement		1,000,000
Average period for PE material purchases under short-term supply contracts for which pricing is negotiated as needed		2 years
Charge recorded		1,471,000	1,144,000
Minimum payments remaining under the Company's lease relating to its reconsidered corporate relocation for 2015		6,753,000
Minimum payments remaining under the Company's lease relating to its reconsidered corporate relocation for 2016		5,490,000
Minimum payments remaining under the Company's lease relating to its reconsidered corporate relocation for 2017		5,370,000
Minimum payments remaining under the Company's lease relating to its reconsidered corporate relocation for 2018		5,308,000
Minimum payments remaining under the Company's lease relating to its reconsidered corporate relocation for 2019		4,467,000
Letters sent to homeowners	10,000
Increase in warranty reserve	20,000,000
Surface Flaking Warranty Reserve [Member]
Schedule Of Commitments And Contingencies [Line Items]
Increase in warranty reserve	20,000,000		20,000,000
Percentage change in warranty claims used as a threshold for disclosure		10.00%
Change in warranty reserve for disclosure purposes only		3,100,000
Residential Use [Member]
Schedule Of Commitments And Contingencies [Line Items]
Warranty period		25 years
Commercial Use [Member]
Schedule Of Commitments And Contingencies [Line Items]
Warranty period		10 years
Transcend, Enhance, Select and Universal Fascia Product [Member] | Residential Use [Member]
Schedule Of Commitments And Contingencies [Line Items]
Warranty period		25 years
Transcend, Enhance, Select and Universal Fascia Product [Member] | Commercial Use [Member]
Schedule Of Commitments And Contingencies [Line Items]
Warranty period		10 years
TrexTrim and Trex Reveal Railing [Member] | Residential Use [Member]
Schedule Of Commitments And Contingencies [Line Items]
Warranty period		25 years
TrexTrim and Trex Reveal Railing [Member] | Commercial Use [Member]
Schedule Of Commitments And Contingencies [Line Items]
Warranty period		25 years
Sublease [Member]
Schedule Of Commitments And Contingencies [Line Items]
Lease square feet		24,732
Contract Termination [Member]
Schedule Of Commitments And Contingencies [Line Items]
Lease square feet		55,047
Charge recorded		1,471,000	1,144,000
Minimum payments remaining under the Company's lease relating to its reconsidered corporate relocation for 2015		1,900,000
Minimum payments remaining under the Company's lease relating to its reconsidered corporate relocation for 2016		1,900,000
Minimum payments remaining under the Company's lease relating to its reconsidered corporate relocation for 2017		2,000,000
Minimum payments remaining under the Company's lease relating to its reconsidered corporate relocation for 2018		2,000,000
Minimum payments remaining under the Company's lease relating to its reconsidered corporate relocation for 2019		1,000,000
Minimum receipts remaining under the Company's existing subleases for 2015		700,000
Minimum receipts remaining under the Company's existing subleases for 2016		600,000
Minimum receipts remaining under the Company's existing subleases for 2017		600,000
Minimum receipts remaining under the Company's existing subleases for 2018		600,000
Minimum receipts remaining under the Company's existing subleases for 2019		400,000
Raw Material Supply Contracts [Member]
Schedule Of Commitments And Contingencies [Line Items]
Purchase commitment		23,600,000
Purchase commitment, due in second year		13,300,000
Purchase commitment, due in third year		5,700,000
Purchase commitment, due in fourth year		48,000
Third Party Manufacturing Contracts [Member]
Schedule Of Commitments And Contingencies [Line Items]
Purchase commitment		$ 1,900,000