Segment Reporting, Geographic Information and Concentration of Credit Risk - Additional Information (Detail) - Customer	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segment Reporting [Abstract]
Concentration Risk, Customer			No customer accounted for 10% or more of net revenue for either of the three or nine months ended September 30, 2019 or 2018. No customer accounted for 10% of net accounts receivable at September 30, 2019 or December 31, 2018.
Number of major customer represented stated percentage of total net revenue	0	0	0	0
Number of customers who accounted for 10% or more net accounts receivable			0		0