Loans - Secured Loans Scheduled Maturities (Details)		3 Months Ended	12 Months Ended
		Mar. 31, 2018 USD ($) MortgageLoan	Dec. 31, 2017 USD ($) MortgageLoan
Secured Loans Scheduled Maturities [Abstract]
2018, Loans | MortgageLoan	[1]	13
2019, Loans | MortgageLoan		37
2020, Loans | MortgageLoan		18
2021, Loans | MortgageLoan		9
2022, Loans | MortgageLoan		11
Thereafter, Loans | MortgageLoan		4
Total future maturities, Loans | MortgageLoan		92
Matured as of March 31, 2018, Loans | MortgageLoan		1
Number of secured loans | MortgageLoan		93	93
2018, Principal | $	[1]	$ 15,156,189
2019, Principal | $		25,167,665
2020, Principal | $		8,254,558
2021, Principal | $		4,244,110
2022, Principal | $		3,469,122
Thereafter, Principal | $		1,434,585
Total future maturities, Principal | $		57,726,229
Matured as of March 31, 2018, Principal | $		139,162
Total secured loan balance, Principal | $		$ 57,865,391	$ 54,768,689
2018, Percent	[1]	26.00%
2019, Percent		43.00%
2020, Percent		14.00%
2021, Percent		7.00%
2022, Percent		6.00%
Thereafter, Percent		3.00%
Total future maturities, Percent		99.00%
Matured as of March 31, 2018, Percent		1.00%
Total secured loan balance, Percent		100.00%	100.00%

[1] Loans maturing in 2018 from April 1 to December 31.