Weighted-Average Assumptions Used to Determine Net Expense For the Plan (Detail)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Qualified Pension Plan
Schedule of Net Periodic Benefit Costs Weighted Average Assumptions [Line Items]
Discount rate	5.85%	6.10%	6.00%
Expected return on plan assets	7.50%	8.00%	8.00%
Qualified Pension Plan | Minimum
Schedule of Net Periodic Benefit Costs Weighted Average Assumptions [Line Items]
Rate of compensation increase	3.50%	4.00%	4.00%
Qualified Pension Plan | Maximum
Schedule of Net Periodic Benefit Costs Weighted Average Assumptions [Line Items]
Rate of compensation increase	5.50%	6.00%	6.00%
Supplemental Executive Retirement Plan (SERP)
Schedule of Net Periodic Benefit Costs Weighted Average Assumptions [Line Items]
Discount rate	5.55%	6.10%	6.00%
Supplemental Executive Retirement Plan (SERP) | Minimum
Schedule of Net Periodic Benefit Costs Weighted Average Assumptions [Line Items]
Rate of compensation increase	3.50%	4.00%	4.00%
Supplemental Executive Retirement Plan (SERP) | Maximum
Schedule of Net Periodic Benefit Costs Weighted Average Assumptions [Line Items]
Rate of compensation increase	5.50%	6.00%	6.00%