Concentrations - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Concentration Risk [Line Items]
Number of customers	5
Top Five Customers
Concentration Risk [Line Items]
Percentage of gross revenues from major customers	82.50%	82.80%	82.60%
Top Five Customers | Customer
Concentration Risk [Line Items]
Percentage of consolidated accounts receivable from major customers	79.70%	85.10%	60.60%