Other Information about Stock Options (Detail) (Employee Stock Option, USD $) In Thousands, except Per Share data, unless otherwise specified	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 [Line Items]
Weighted-average estimated grant-date fair value of employee stock options granted (per share)	$ 20.10		$ 25.81
Total pre-tax intrinsic value of stock options exercised	$ 303	$ 2,903	$ 2,489	$ 7,435
Pre-tax unrecognized compensation expense, net of estimated forfeitures as of June 30, 2012	$ 6,190		$ 6,190
Weighted-average period (in years) to be recognized as expense			2 years 2 months 12 days