Retirement and Deferred Compensation Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Contribution Benefit Plans [Line Items]
Description of 401 (K)	The 2011 annual 401(k) deferral limit for employees under age 50 was $16,500. Employees turning age 50 or over in 2011 could defer up to $22,000 in 2011. The Company makes matching contributions to the plan equal to 100% on the first 15% of employee deferred wages.
Percentage matching contributions from employer on the first 15% of employee deferred wages	100.00%
Retirement plan expense	$ 7,400,000	$ 8,700,000	$ 7,400,000
Employer contributions to deferred compensation plan	3,100,000	2,800,000	2,500,000
Employees under age 50
Defined Contribution Benefit Plans [Line Items]
Maximum annual amount employee could defer	16,500
Employees turning age 50 or over
Defined Contribution Benefit Plans [Line Items]
Maximum annual amount employee could defer	$ 22,000
Maximum
Defined Contribution Benefit Plans [Line Items]
Percentage of employee gross earnings employer makes matching contributions on for the non-qualified deferred compensation plan	15.00%