Employee Benefit Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 20,800,000
Upper limit of employer match	4.00%
Criteria of employer to contribute in employee Saving Plan	100% of an employee's first 3% of contributions and 50% of their next 2% of contributions
Percentage of employer match to employee's first 3 % contribution	100.00%
Percentage of employer match to the next 2% of contributions	50.00%
Maximum statutory compensation under code	250,000
Percentage contributions under the Savings Plan, vested	100.00%
Contributions and plan administration costs for Savings Plan	4,600,000	4,300,000	4,600,000
Maximum percentage of cash compensation allowed to be deferred under the Deferred Compensation Plan	25.00%
Criteria for benefit distribution	Six months after termination of employment in a single lump sum payment
Deferred compensation adjustments due to fair value of the trust assets	900,000	(200,000)	400,000
Maximum number of years medical, dental and prescription drug coverage to spouse of deceased officer	30 years
Total liability recorded to provide medical, dental and prescription drug coverage	$ 200,000	$ 200,000
Bond funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of target allocation ranges by asset class	75.00%
Equity funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of target allocation ranges by asset class	25.00%