Reconciliation between Federal Statutory Rate and Effective Tax Rate (Detail)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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	2.30%	2.50%	3.00%
Nondeductible transaction costs			0.20%
Divestiture gain		0.30%
Other items		0.40%	0.10%
Impact of income attributable to noncontrolling interests	(2.40%)	(1.90%)	(2.30%)
Effective tax rate	34.90%	36.30%	36.00%

Effective income tax rate reconciliation impact of income attributable to noncontrolling interest.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to disposition of a business not qualifying as a discontinued operation.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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