Employee Savings Plan - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Benefit Plans [Line Items]
Number of days of service required for employee to participate	30 days
Employer contributions to plan, maximum percentage	2.50%
Discretionary profit-sharing contribution percentage for each past three years based on employee's compensation	1.50%
Employer contributions to the plan	$ 14,266,000	$ 11,866,000	$ 11,376,000