Reconciliation of Denominator for Basic and Diluted Earnings Per Share (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Weighted average common shares-basic	66,298,633	65,999,090	66,203,965	65,873,023
Plus incremental shares from: Assumed exercise of options	350,263	425,975	399,741	396,800
Weighted average common shares-diluted	66,648,896	66,425,065	66,603,706	66,269,823
Earnings per share: Basic	$ 1.73	$ 1.22	$ 3.05	$ 2.48
Earnings per share: Diluted	$ 1.72	$ 1.21	$ 3.03	$ 2.46