Weighted Average Assumptions for Option Awards Granted (Detail) (Employee Stock Option)	3 Months Ended			6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award
Expected volatility		[1]	34.00%	36.00%	34.00%
Expected term (in years)		[1]	5 years 3 months 18 days	5 years 8 months 12 days	5 years 8 months 12 days
Risk-free interest rate		[1]	1.90%	1.00%	2.10%
Expected dividend yield		[1]

[1] No options were granted during the three months ended June 30, 2012.