Fair Value Measurements Available for sale securities (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	$ 730,475,386		$ 730,475,386		$ 730,475,386	$ 668,651,258
Assets at Fair Value			668,651,258
Total gains (losses) (realized/unrealized) [Abstract]
Assets at Fair Value	730,475,386		730,475,386
Estimated Fair Value, held in trust					61,105,457	47,366,656
Fair Value, Inputs, Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value Observable inputs (level 2)						14,775,309
Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	666,958,282	$ 577,144,337	730,475,386	$ 613,079,147	730,475,386	653,875,949
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value					730,475,386	653,875,949
Assets at Fair Value	666,958,282	577,144,337	653,875,949	520,951,907
Total gains (losses) (realized/unrealized) [Abstract]
Gain (Loss) on Investments	(531,389)	198,743	(1,641,796)	(701,130)
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities	69,830,975	(21,297,364)	83,756,215	(22,980,872)
Refund of interest rate derivative cost				(10,500)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(5,782,483)	(16,006,569)	(7,267,459)	(16,165,258)
Assets at Fair Value	730,475,386	613,079,147	730,475,386	613,079,147
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		73,040,000	11,500,000	131,985,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sale of securities			(9,747,523)
Mortgage Revenue Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	648,397,372		648,397,372		648,397,372	583,683,137
Assets at Fair Value			583,683,137
Total gains (losses) (realized/unrealized) [Abstract]
Assets at Fair Value	648,397,372		648,397,372
Mortgage Revenue Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	596,376,369	507,898,698	648,397,372	548,935,985	648,397,372	583,683,137
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value					648,397,372	583,683,137
Assets at Fair Value	596,376,369	507,898,698	583,683,137	449,024,137
Total gains (losses) (realized/unrealized) [Abstract]
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities	57,767,098	(16,544,139)	69,118,725	(16,469,539)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(5,746,096)	(14,958,574)	(6,157,366)	(15,103,613)
Assets at Fair Value	648,397,372	548,935,985	648,397,372	548,935,985
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		72,540,000	11,500,000	131,485,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sale of securities			(9,747,124)
Bond Purchase Commitment [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	17,218,819		17,218,819		17,218,819	5,634,360
Assets at Fair Value			5,634,360
Total gains (losses) (realized/unrealized) [Abstract]
Assets at Fair Value	17,218,819		17,218,819
Bond Purchase Commitment [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	7,222,173	5,204,188	17,218,819	883,999	17,218,819	5,634,360
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value					17,218,819	5,634,360
Assets at Fair Value	7,222,173	5,204,188	5,634,360	5,780,413
Total gains (losses) (realized/unrealized) [Abstract]
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities	9,996,646	(4,320,189)	11,584,459	(4,896,414)
Assets at Fair Value	17,218,819	883,999	17,218,819	883,999
PHC Certificates [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	62,180,059		62,180,059		62,180,059	60,707,290
Assets at Fair Value			60,707,290
Total gains (losses) (realized/unrealized) [Abstract]
Assets at Fair Value	62,180,059		62,180,059
PHC Certificates [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	60,505,340	60,272,941	62,180,059	58,991,437	62,180,059	60,707,290
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value					62,180,059	60,707,290
Assets at Fair Value	60,505,340	60,272,941	60,707,290	61,263,123
Total gains (losses) (realized/unrealized) [Abstract]
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities	1,688,370	(304,327)	2,557,714	(1,280,859)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(13,651)	(977,177)	(1,084,945)	(990,827)
Assets at Fair Value	62,180,059	58,991,437	62,180,059	58,991,437
Taxable Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	5,294,229		5,294,229		5,294,229	4,824,060
Assets at Fair Value			4,824,060
Total gains (losses) (realized/unrealized) [Abstract]
Assets at Fair Value	5,294,229		5,294,229
Taxable Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	4,938,104	4,411,214	5,294,229	4,711,687	5,294,229	4,824,060
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value					5,294,229	4,824,060
Assets at Fair Value	4,938,104	4,411,214	4,824,060	4,616,565
Total gains (losses) (realized/unrealized) [Abstract]
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities	378,861	(128,709)	495,317	(334,060)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(22,736)	(70,818)	(25,148)	(70,818)
Assets at Fair Value	5,294,229	4,711,687	5,294,229	4,711,687
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		500,000		500,000
Interest rate derivatives [Member]
Schedule of Available-for-sale Securities [Line Items]
Liabilities at fair value	(2,615,094)		(2,615,094)		(2,615,094)	(972,898)
Liabilities at fair value			(972,898)
Total gains (losses) (realized/unrealized) [Abstract]
Liabilities at fair value	(2,615,094)		(2,615,094)
Interest rate derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value				267,669
Liabilities at fair value	(2,083,704)	(642,704)	(2,615,094)	(443,961)	(2,615,094)	(972,898)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liabilities Value					$ (2,615,094)	(972,898)
Assets at Fair Value				267,669
Liabilities at fair value	(2,083,704)	(642,704)	(972,898)
Total gains (losses) (realized/unrealized) [Abstract]
Gain (Loss) on Investments	(531,389)	198,743	(1,641,796)	(701,130)
Refund of interest rate derivative cost				(10,500)
Liabilities at fair value	$ (2,615,094)	$ (443,961)	(2,615,094)	$ (443,961)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sale of securities			(399)
MBS Securities
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value			14,775,309			14,775,309
Assets at Fair Value			$ 14,775,309
MBS Securities | Fair Value, Inputs, Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value Observable inputs (level 2)						$ 14,775,309