Accounts Receivable - Additional Information (Detail) - Distributor	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Receivables [Abstract]
Number of wholesale distributors	3	3	3
Percentage of accounts receivable from major wholesale distributors	92.00%	92.00%	93.00%