Concentration of Risks - Additional Information (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Total revenue [Member]
Product Information [Line Items]
Number of customers represented more than 10%	0	0
Total accounts receivable [Member]
Product Information [Line Items]
Number of customers represented more than 10%	1	0