Reconciliation Of Income Tax Provision At Statutory Income Tax Rate And Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of Provision of Income Taxes [Line Items]
Statutory federal rate	35.00%	35.00%	35.00%
State taxes, net of federal tax benefit	1.00%	2.60%	2.70%
Permanent differences	0.70%	0.50%	0.70%
Change in valuation allowance	0.00%	0.10%	(0.10%)
Changes in tax contingencies	0.00%	(0.10%)	0.00%
Other items, net	(0.90%)	(0.90%)	(0.90%)
Effective income tax rate, Total	35.80%	37.20%	37.40%