Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018
Significant Accounting Policies [Line Items]
Standard warranty period	12 months
Minimum
Significant Accounting Policies [Line Items]
Extended warranty period	12 months
Maximum
Significant Accounting Policies [Line Items]
Extended warranty period	36 months