Summary of Significant Accounting Policies - Schedule of Customers Representing Greater than 10% of Accounts Receivable and Revenue (Detail) - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue | Customer A
Concentration Risk [Line Items]
Percentage of concentration risk	17.00%
Revenue | Customer B
Concentration Risk [Line Items]
Percentage of concentration risk	17.00%
Revenue | Customer C
Concentration Risk [Line Items]
Percentage of concentration risk	16.00%		48.00%
Revenue | Customer D
Concentration Risk [Line Items]
Percentage of concentration risk	16.00%
Revenue | Customer E
Concentration Risk [Line Items]
Percentage of concentration risk	14.00%
Revenue | Customer F
Concentration Risk [Line Items]
Percentage of concentration risk	10.00%
Revenue | Customer H
Concentration Risk [Line Items]
Percentage of concentration risk		47.00%
Revenue | Customer I
Concentration Risk [Line Items]
Percentage of concentration risk		25.00%
Revenue | Customer J
Concentration Risk [Line Items]
Percentage of concentration risk		23.00%
Revenue | Customer K
Concentration Risk [Line Items]
Percentage of concentration risk			43.00%
Accounts Receivable | Customer D
Concentration Risk [Line Items]
Percentage of concentration risk	24.00%
Accounts Receivable | Customer E
Concentration Risk [Line Items]
Percentage of concentration risk	16.00%
Accounts Receivable | Customer G
Concentration Risk [Line Items]
Percentage of concentration risk	36.00%
Accounts Receivable | Customer H
Concentration Risk [Line Items]
Percentage of concentration risk		49.00%
Accounts Receivable | Customer J
Concentration Risk [Line Items]
Percentage of concentration risk		41.00%