Segment Data - Additional Information (Detail) (Outside of United States [Member])	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Outside of United States [Member]
Segment Reporting Information [Line Items]
Percentage of revenue generated from the foreign countries	5.70%	3.40%	1.00%
Percentage of total assets in the foreign countries	12.20%	8.70%