Schedule of Reconciliation Between Federal Statutory Rate and Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of Statutory Federal Tax Rate [Line Items]
Federal statutory rate	35.00%	35.00%	35.00%
State taxes, net of federal income tax benefit	3.00%	2.90%	3.10%
Nondeductible transaction costs	0.20%		1.30%
Other items	0.10%	0.40%	0.40%
Impact of income attributable to noncontrolling interests	(2.30%)	(2.80%)	(4.20%)
Effective tax rate	36.00%	35.50%	35.60%