Debt Financing - Schedule of Total Debt Financing (Details) - USD ($)		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Short Term Debt [Line Items]
Debt financing		$ 550,425,793	$ 558,328,347
Period End Rates		4.38%	4.21%
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term TOB [Member]
Short Term Debt [Line Items]
Debt financing		$ 46,759,131	$ 46,787,036
Year Acquired		2014	2014
Stated Maturities		2019-10	2019-10
Reset Frequency		N/A	N/A
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term TOB [Member] | Minimum [Member]
Short Term Debt [Line Items]
Period End Rates		4.01%	4.01%
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term TOB [Member] | Maximum [Member]
Short Term Debt [Line Items]
Period End Rates		4.39%	4.39%
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B I [Member]
Short Term Debt [Line Items]
Debt financing		$ 26,341,166	$ 33,612,154
Year Acquired		2017	2017
Reset Frequency		N/A	N/A
Period End Rates		3.76%	3.76%
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B I [Member] | Minimum [Member]
Short Term Debt [Line Items]
Stated Maturities		2018-06	2018-06
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B I [Member] | Maximum [Member]
Short Term Debt [Line Items]
Stated Maturities		2018-08	2018-08
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B [Member]
Short Term Debt [Line Items]
Debt financing		$ 60,466,647	$ 60,441,915
Year Acquired		2017	2017
Reset Frequency		N/A	N/A
Period End Rates		3.89%	3.76%
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B [Member] | Minimum [Member]
Short Term Debt [Line Items]
Stated Maturities		2022-02	2022-02
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B [Member] | Maximum [Member]
Short Term Debt [Line Items]
Stated Maturities		2022-03	2022-03
TOB & Term A/B Trusts Securitization [Member] | Variable - TOB [Member]
Short Term Debt [Line Items]
Debt financing		$ 37,965,000	$ 38,130,000
Restricted Cash		$ 377,361	$ 850,327
Year Acquired		2012	2012
Stated Maturities		2018-05	2018-05
Reset Frequency		Weekly	Weekly
Facility Fees		1.67%	1.67%
TOB & Term A/B Trusts Securitization [Member] | Variable - TOB [Member] | Minimum [Member]
Short Term Debt [Line Items]
SIFMA Based Rates		2.11%	2.24%
Period End Rates		3.78%	3.91%
TOB & Term A/B Trusts Securitization [Member] | Variable - TOB [Member] | Maximum [Member]
Short Term Debt [Line Items]
SIFMA Based Rates		2.16%	2.29%
Period End Rates		3.83%	3.96%
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B III [Member]
Short Term Debt [Line Items]
Debt financing		$ 137,923,057	$ 138,065,482
Year Acquired		2016	2016
Reset Frequency		N/A	N/A
Period End Rates		3.64%	3.64%
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B III [Member] | Minimum [Member]
Short Term Debt [Line Items]
Stated Maturities		2026-09	2026-09
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B III [Member] | Maximum [Member]
Short Term Debt [Line Items]
Stated Maturities		2026-12	2026-12
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B IV [Member]
Short Term Debt [Line Items]
Debt financing		$ 47,408,991	$ 47,414,014
Year Acquired		2017	2017
Reset Frequency		N/A	N/A
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B IV [Member] | Minimum [Member]
Short Term Debt [Line Items]
Stated Maturities		2027-02	2027-02
Period End Rates		4.46%	4.46%
TOB & Term A/B Trusts Securitization [Member] | Fixed - Term A/B IV [Member] | Maximum [Member]
Short Term Debt [Line Items]
Stated Maturities		2027-11	2027-11
Period End Rates		4.52%	4.52%
TEBS Financings [Member] | Variable - TEBS I [Member]
Short Term Debt [Line Items]
Debt financing		$ 55,334,000	$ 55,468,000
Restricted Cash		$ 27,747	$ 372,222
Year Acquired		2010	2010
Stated Maturities		2020-09	2020-09
Reset Frequency		Weekly	Weekly
SIFMA Based Rates		1.69%	1.79%
Facility Fees		1.85%	1.85%
Period End Rates		3.54%	3.64%
TEBS Financings [Member] | Variable - TEBS II [Member]
Short Term Debt [Line Items]
Debt financing	[1]	$ 80,876,101	$ 81,003,688
Restricted Cash	[1]	$ 136,626	$ 176,685
Year Acquired	[1]	2014	2014
Stated Maturities	[1]	2019-07	2019-07
Reset Frequency	[1]	Weekly	Weekly
SIFMA Based Rates	[1]	1.66%	1.77%
Facility Fees	[1]	1.51%	1.39%
Period End Rates	[1]	3.17%	3.16%
TEBS Financings [Member] | Variable - TEBS III [Member]
Short Term Debt [Line Items]
Debt financing	[1]	$ 57,351,700	$ 57,406,058
Restricted Cash	[1]	$ 56,111	$ 57,364
Year Acquired	[1]	2015	2015
Stated Maturities	[1]	2020-07	2020-07
Reset Frequency	[1]	Weekly	Weekly
SIFMA Based Rates	[1]	1.66%	1.77%
Facility Fees	[1]	1.28%	1.16%
Period End Rates	[1]	2.94%	2.93%

[1] Facility fees are variable