Summary of Significant Accounting Policies - Narrative - Restricted Cash (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Restricted cash, excluding restricted cash held-for-sale	$ 12,114,277	$ 28,959,004
Restricted cash and cash equivalents, held by intermediaries for purposes of facilitating a 1031 exchange	0	17,197,810
Restricted cash and cash equivalents, debt covenant, held in impound for future expenses	12,114,277	11,761,194
Beginning cash balances included in assets held for sale	$ 4,908,519	$ 12,086,960	$ 0