Concentration of Risks - Additional Information (Detail) - Customer	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Customer Concentration Risk [Member] | Total revenue [Member]
Concentration Risk [Line Items]
Number of customer that individually represented more than 10% of total revenue and accounts receivable	1	0	0	0
Customer Concentration Risk [Member] | Total revenue [Member] | Minimum [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%	10.00%	10.00%	10.00%
Credit Concentration Risk [Member] | Total accounts receivable [Member]
Concentration Risk [Line Items]
Number of customer that individually represented more than 10% of total revenue and accounts receivable			0		1
Credit Concentration Risk [Member] | Total accounts receivable [Member] | Minimum [Member]
Concentration Risk [Line Items]
Concentration risk, percentage			10.00%		10.00%