Investments in Mortgage Revenue Bonds ("MRBs") - Additional Information (Details)	9 Months Ended
	Sep. 30, 2018 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Contingent interest income	$ 4,246,094
Mortgage Revenue Bonds [Member] | Lake Forest [Member] | Daytona Florida [Member]
Schedule Of Available For Sale Securities [Line Items]
Contingent interest income	4,200,000
Mortgage Revenue Bonds [Member] | Lake Forest [Member] | Daytona Florida [Member] | Other Income [Member]
Schedule Of Available For Sale Securities [Line Items]
Gain on early redemption of mortgage revenue bonds	$ 1,500,000