Commitments and Contingencies - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Schedule Of Commitments And Contingencies [Line Items]
Change in warranty reserve for disclosure purposes only	$ 2.5
Minimum [Member]
Schedule Of Commitments And Contingencies [Line Items]
Warranty period	10 years
Maximum [Member]
Schedule Of Commitments And Contingencies [Line Items]
Warranty period	25 years
Surface Flaking Warranty Reserve [Member]
Schedule Of Commitments And Contingencies [Line Items]
Percentage change in warranty claims used as a threshold for disclosure	10.00%