Commitments and Contingencies - Additional Information (Detail) - Customer	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Sales Revenue, Net [Member]
Commitments And Contingencies [Line Items]
Number of customers	3	2
Accounts Receivable [Member]
Commitments And Contingencies [Line Items]
Number of customers	3		2
Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Commitments And Contingencies [Line Items]
Concentration risk, percentage		17.00%
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Due From Related Party [Member]
Commitments And Contingencies [Line Items]
Concentration risk, percentage		24.00%
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | One Customer [Member]
Commitments And Contingencies [Line Items]
Concentration risk, percentage	15.00%
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Three Customer [Member]
Commitments And Contingencies [Line Items]
Concentration risk, percentage	11.00%
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Two Customers [Member]
Commitments And Contingencies [Line Items]
Concentration risk, percentage	13.00%
Customer Concentration Risk [Member] | Accounts Receivable [Member] | One Customer [Member]
Commitments And Contingencies [Line Items]
Concentration risk, percentage	20.00%		20.00%
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Three Customer [Member]
Commitments And Contingencies [Line Items]
Concentration risk, percentage	16.00%
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Two Customers [Member]
Commitments And Contingencies [Line Items]
Concentration risk, percentage	20.00%		16.00%