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Income Taxes - Narrative (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 6,496,980	$ 7,700,732	$ 19,018,708	$ 18,497,315
Effective tax rate	33.10%	36.00%	32.60%	36.10%
Federal statutory income tax rate, percent	35.00%	35.00%	35.00%	35.00%
Effective income tax rate reconciliation, share-based compensation, excess tax benefit (tax shortfall), Amount	$ 400,000		$ 1,700,000
Effective income tax rate reconciliation, tax benefit due to donation of appreciated securities, Amount				$ 100,000
Income tax effects allocated directly to equity		$ (200,000)		$ (5,600,000)
Valuation allowance	$ 0		$ 0		$ 0

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- Definition

Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit (Tax Shortfall), Amount

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Effective Income Tax Rate Reconciliation, Tax Benefit Due To Donation Of Appreciated Securities, Amount

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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-Publisher FASB
-Name Accounting Standards Codification
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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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The sum of the tax effects of all items occurring during the period that have been charged or credited directly to other comprehensive income or to related components of shareholders' equity.

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

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