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Income Taxes - Reconciliation of Income Tax Expense to Federal Statutory Rate (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of reconciliation of income tax expense
Income tax computed at statutory rate	$ 28,356,636	$ 25,641,618	$ 20,294,107
Benefit attributable to redeemable noncontrolling interests	(564,449)	(189,773)	0
City and state income taxes, net of federal benefit	1,153,357	1,276,777	1,027,768
Revaluation adjustment of net deferred tax assets	3,557,039	0	0
Excess tax benefits on vesting of Restricted Stock	(2,420,250)	0	0
Income tax benefit from dividends paid on Restricted Stock	(418,583)	0	0
Other	(246,460)	(60,987)	(413,210)
Provision for income taxes	$ 29,417,290	$ 26,667,635	$ 20,908,665

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

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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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Amount 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 deduction for dividend.

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