Concentration Risk - Additional Information (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Concentration Risk [Line Items]
Number of customer accounting for more than ten percent of accounts receivable	2	2
Customer One
Concentration Risk [Line Items]
Percentage of accounts receivable from one customer out of total accounts receivable	19.00%	23.00%
Customer Two
Concentration Risk [Line Items]
Percentage of accounts receivable from one customer out of total accounts receivable	10.00%	11.00%
Customer Concentration Risk
Concentration Risk [Line Items]
Percentage of revenue from one customer out of total revenue		19.00%
Number of customer accounting for more than ten percent of revenue		1