Debt Financing Total Debt Financing (Details) - Trading Securities [Member] - USD ($)		3 Months Ended	12 Months Ended
		Mar. 31, 2016	Dec. 31, 2015
Short Term Debt [Line Items]
TOB Trust Financing		$ 195,303,919	$ 216,512,124
Debt Instrument, Total Rate of Borrowing		3.42%	3.26%
TOB facility-2 [Member]
Short Term Debt [Line Items]
TOB Trust Financing	[1]	$ 43,145,000	$ 43,985,000
Date of Debt Borrowing	[1]	2012	2012
Available-for-sale Security, Maturity Date at a point in time	[1]	Jun. 01, 2016	Jun. 01, 2016
Debt Instrument, Interest rate terms	[1]	Variable	Variable
Debt Instrument, Reset Frequency	[1]	Weekly	Weekly
Debt Instrument, Basis Spread on Variable Rate	[1]	0.95%	0.68%
Debt Instrument, Facility Fees	[1]	1.62%	1.62%
Debt Instrument, Total Rate of Borrowing	[1]	2.57%	2.30%
TOB Facility-10 [Member]
Short Term Debt [Line Items]
TOB Trust Financing		$ 22,848,215	$ 22,847,450
Date of Debt Borrowing		2014	2014
Available-for-sale Security, Maturity Date at a point in time		Oct. 01, 2016	Oct. 01, 2016
Debt Instrument, Interest rate terms		Fixed	Fixed
Debt Instrument, Reset Frequency		N/A	N/A
Debt Instrument, Total Rate of Borrowing		4.26%	4.26%
TOB Facility-11 [Member]
Short Term Debt [Line Items]
TOB Trust Financing		$ 37,911,261	$ 37,935,981
Date of Debt Borrowing		2014	2014
Available-for-sale Security, Maturity Date at a point in time		Jul. 01, 2019	Jul. 01, 2019
Debt Instrument, Interest rate terms		Fixed	Fixed
Debt Instrument, Reset Frequency		N/A	N/A
Debt Instrument, Total Rate of Borrowing		4.39%	4.39%
TOB Facility-12 [Member] [Member]
Short Term Debt [Line Items]
TOB Trust Financing		$ 17,247,389	$ 17,246,899
Date of Debt Borrowing		2014	2014
Available-for-sale Security, Maturity Date at a point in time		Jul. 01, 2017	Jul. 01, 2017
Debt Instrument, Interest rate terms		Fixed	Fixed
Debt Instrument, Reset Frequency		N/A	N/A
Debt Instrument, Total Rate of Borrowing		4.51%	4.51%
TOB facility-13 [Member]
Short Term Debt [Line Items]
TOB Trust Financing		$ 9,007,389	$ 9,006,899
Date of Debt Borrowing		2014	2014
Available-for-sale Security, Maturity Date at a point in time		Jul. 01, 2017	Jul. 01, 2017
Debt Instrument, Interest rate terms		Fixed	Fixed
Debt Instrument, Reset Frequency		N/A	N/A
Debt Instrument, Total Rate of Borrowing		4.01%	4.01%
TOB Facility-15 [Member]
Short Term Debt [Line Items]
TOB Trust Financing		$ 14,937,068	$ 14,936,685
Date of Debt Borrowing		2015	2015
Available-for-sale Security, Maturity Date at a point in time		Feb. 01, 2018	Feb. 01, 2018
Debt Instrument, Interest rate terms		Fixed	Fixed
Debt Instrument, Reset Frequency		N/A	N/A
Debt Instrument, Total Rate of Borrowing		2.76%	2.76%
TOB Facility-16 [Member]
Short Term Debt [Line Items]
TOB Trust Financing		$ 11,232,068	$ 11,231,685
Date of Debt Borrowing		2015	2015
Available-for-sale Security, Maturity Date at a point in time		Feb. 01, 2018	Feb. 01, 2018
Debt Instrument, Interest rate terms		Fixed	Fixed
Debt Instrument, Reset Frequency		N/A	N/A
Debt Instrument, Total Rate of Borrowing		2.76%	2.76%
TOB Facility-17 [Member]
Short Term Debt [Line Items]
TOB Trust Financing		$ 15,607,068	$ 15,606,685
Date of Debt Borrowing		2015	2015
Available-for-sale Security, Maturity Date at a point in time		Feb. 01, 2018	Feb. 01, 2018
Debt Instrument, Interest rate terms		Fixed	Fixed
Debt Instrument, Reset Frequency		N/A	N/A
Debt Instrument, Total Rate of Borrowing		2.76%	2.76%
TOB Facility-18 [Member]
Short Term Debt [Line Items]
TOB Trust Financing		$ 11,684,439	$ 11,699,209
Date of Debt Borrowing		2015	2015
Available-for-sale Security, Maturity Date at a point in time		Dec. 01, 2017	Dec. 01, 2017
Debt Instrument, Interest rate terms		Fixed	Fixed
Debt Instrument, Reset Frequency		N/A	N/A
Debt Instrument, Total Rate of Borrowing		2.76%	2.76%
TOB Facility-19 [Member]
Short Term Debt [Line Items]
TOB Trust Financing		$ 11,684,022	$ 11,698,732
Date of Debt Borrowing		2015	2015
Available-for-sale Security, Maturity Date at a point in time		Dec. 01, 2017	Dec. 01, 2017
Debt Instrument, Interest rate terms		Fixed	Fixed
Debt Instrument, Reset Frequency		N/A	N/A
Debt Instrument, Total Rate of Borrowing		2.76%	2.76%
TOB facility-3 [Member] | Mortgage Backed Security 1 [Member]
Short Term Debt [Line Items]
TOB Trust Financing			$ 2,585,000
Date of Debt Borrowing			2012
Available-for-sale Security, Maturity Date at a point in time			Apr. 01, 2016
Debt Instrument, Interest rate terms			Variable
Debt Instrument, Reset Frequency			Weekly
Debt Instrument, Basis Spread on Variable Rate			0.16%
Debt Instrument, Facility Fees			0.94%
Debt Instrument, Total Rate of Borrowing			1.10%
TOB facility-3 [Member] | Mortgage Backed Security 2 [Member]
Short Term Debt [Line Items]
TOB Trust Financing			$ 4,090,000
Date of Debt Borrowing			2012
Available-for-sale Security, Maturity Date at a point in time			Apr. 01, 2016
Debt Instrument, Interest rate terms			Variable
Debt Instrument, Reset Frequency			Weekly
Debt Instrument, Basis Spread on Variable Rate			0.16%
Debt Instrument, Facility Fees			0.94%
Debt Instrument, Total Rate of Borrowing			1.10%
TOB facility-3 [Member] | Mortgage Backed Security Trust 3 [Member]
Short Term Debt [Line Items]
TOB Trust Financing			$ 5,270,000
Date of Debt Borrowing			2012
Available-for-sale Security, Maturity Date at a point in time			Apr. 01, 2016
Debt Instrument, Interest rate terms			Variable
Debt Instrument, Reset Frequency			Weekly
Debt Instrument, Basis Spread on Variable Rate			0.16%
Debt Instrument, Facility Fees			0.94%
Debt Instrument, Total Rate of Borrowing			1.10%
TOB Facility-14 [Member]
Short Term Debt [Line Items]
TOB Trust Financing			$ 8,371,899
Date of Debt Borrowing			2014
Available-for-sale Security, Maturity Date at a point in time			Jul. 01, 2017
Debt Instrument, Interest rate terms			Fixed
Debt Instrument, Reset Frequency			N/A
Debt Instrument, Total Rate of Borrowing			4.01%

[1] Comprised of three TOB Trusts