Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2019	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Interest and/or penalties related to income tax matters	$ 0	$ 0	$ 0	$ 0
Securities available for sale, at fair value	(46,324,158)		(46,324,158)				$ (41,471,711)
Other investments	7,220,880		7,220,880				4,286,500
Assets	1,035,028,184		1,035,028,184				900,998,830
Liabilities	$ 910,053,031		$ 910,053,031				$ 809,518,880
ASU 2016-01
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Securities available for sale, at fair value						$ 2,500,000
Other investments						$ 2,500,000
ASU 2016-02
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Assets					$ 13,000,000
Liabilities					$ 13,000,000
Equipment and Furnishings | Minimum
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Equipment and furnishings, useful lives			3 years
Equipment and Furnishings | Maximum
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Equipment and furnishings, useful lives			10 years