Concentration of Risks - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2015 Customer	Mar. 31, 2014 Customer	Dec. 31, 2014 Customer
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	0	1
Customer Concentration Risk [Member] | Total revenue [Member] | Minimum [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	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	1		1
Credit Concentration Risk [Member] | Total accounts receivable [Member] | Minimum [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%		10.00%