Income Taxes - Reconciliation of U.S. Federal Statutory Tax Rate to Company's Effective Tax Rate (Detail)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. federal statutory rate	21.00%	35.00%	35.00%
State taxes, net of federal benefit	5.00%	4.10%	4.20%
State deferred tax rate change, net of federal benefit	0.70%	0.50%	2.00%
Valuation allowance	(0.50%)	0.10%	1.10%
Share-based compensation	(1.90%)	(1.00%)
Enactment of the Tax Cuts and Jobs Act	(0.10%)	(122.90%)
Other	0.00%	(0.20%)	0.60%
Effective Income Tax Rate	24.20%	(84.40%)	42.90%

Effective income tax rate reconciliation deductible expense share-based compensation cost income tax purposes percent.

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- Definition

Effective income tax rate reconciliation deferred tax change in state and local income taxes.

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Tax cuts and jobs act of 2017 change in tax rate percentage.

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- Definition

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 changes in the valuation allowance for deferred tax assets.

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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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